The bedouin nomads have never had a state or government, yet are considered a distinct ethnicity, even if they are spread all over the Middle East.
Just as another example: Prior to the 16th century, 'American' was generally used to refer to the native Indian population. It wasn't until the 17th century that European settlers began to adopt the term as a common descriptor; shortly after our own independence, 'American' came to be the common demonym for citizens of the United States, and the native Indians were no longer commonly called 'Americans' anymore; referring to Americans by the European origin (whether British, French, etc) was discouraged.
The lesson is that nationalist fervor can emerge in a relatively short time, especially if the pressure is high enough: given that the various Palestinians have been 'de facto' treated as a separate class of people by both Israel and the other Arab/Islamic states surrounding them, are you shocked that they would adopt the demonym?
Often seen is a claim that modern Israel won a war of independence in 1948. If so, who did they become independent from? Modern Israel was created by Great Britain and the League of Nations/United Nations. Unclear is how the UN owned the land, or had the authority to give it to Israel. Under the League of Nations, Britain was the appointed administrator of the Mandate for Palestine.
https://en.wikipedia.org/wiki/History_of_ancient_Israel_and_Judah
According to the Hebrew Bible, a "United Monarchy" (consisting of Israel and Judah) existed as early as the 11th century BCE, under the reigns of Saul, David, and Solomon; the country later split into two kingdoms: Israel, containing the cities of Shechem and Samaria in the north, and Judah (containing Jerusalem and the Jewish Temple) in the south. The historicity of the United Monarchy is debated—as there are no archaeological remains of it that are accepted as consensus—but The Kingdom of Israel was destroyed around 720 BCE, when it was conquered by the Neo-Assyrian Empire. While the Kingdom of Judah remained intact during this time, it became a client state of first the Neo-Assyrian Empire and then the Neo-Babylonian Empire. However, Jewish revolts against the Babylonians led to the destruction of Judah in 586 BCE, under the rule of Babylonian king Nebuchadnezzar II. According to the biblical account, the armies of Nebuchadnezzar II besieged Jerusalem between 589–586 BCE, which led to the destruction of Solomon's Temple and the exile of the Jews to Babylon; this event was also recorded in the Babylonian Chronicles. The exilic period, saw the development of the Israelite religion (Yahwism) towards the monotheistic Judaism.This ended with the fall of Babylon to the Achaemenid Persian Empire around 538 BCE. Subsequently, Persian king Cyrus the Great issued a proclamation known as the Edict of Cyrus, which authorized and encouraged exiled Jews to return to Judah. Cyrus' proclamation began the exiles' return to Zion, inaugurating the formative period in which a more distinctive Jewish identity developed in the Persian province of Yehud. During this time, the destroyed Solomon's Temple was replaced by the Second Temple, marking the beginning of the Second Temple period.
https://www.loc.gov/item/2021666887/
TitleMandate for Palestine and Memorandum by the British Government Relating to its Application to Transjordan.
Summary
After World War I, the Covenant of the League of Nations established a system by which the League was empowered to confer upon certain of the victorious powers mandates to administer territories formerly ruled by Germany or the Ottoman Empire. Mandated territories were to be governed on behalf of the League, until such time as they could become independent. On September 16, 1922, the Council of the League approved a mandate to Great Britain for Palestine, previously part of the Ottoman Empire. The mandate provided for the eventual creation of a Jewish state, as specified in Article 2: "The Mandatory shall be responsible for placing the country under such political, administrative and economic conditions as will secure the establishment of a Jewish national home, as laid down in the preamble, and the development of self-governing institutions, and also for safeguarding the civil and religious rights of all the inhabitants of Palestine, irrespective of race and religion." Successive articles dealt with Jewish immigration, public administration, access to holy places and religious buildings, public health, commerce, and other matters. Appended to the mandate was a memorandum by the British government, also approved by the Council of the League, stating its understanding that the provisions of the mandate relating to the establishment of a Jewish national home and the promotion of Jewish immigration were not to apply to that portion of the mandated territory known as Transjordan, i.e., territory east of the Jordan River. The texts are in French and English, on facing pages. The mandate is in the archives of the League, which were transferred to the United Nations in 1946 and are housed at the UN office in Geneva. The archives were inscribed on the UNESCO Memory of the World register in 2010.