WIKI
in 1843, the term Ruthenian became the official name for the Rusyns and Ukrainians within the Austrian Empire. For example, Ivan Franko and Stepan Bandera in their passports were identified as Ruthenians (Polish: Rusini). By 1900, more and more Ruthenians began to call themselves with the self-designated name Ukrainians. With the emergence of Ukrainian nationalism during the mid-19th century, use of “Ruthenian” and cognate terms declined among Ukrainians and fell out of use in Eastern and Central Ukraine. Most people in the western region of Ukraine followed suit later in the 19th century. During the early 20th century, the name Ukrajins’ka mova (”Ukrainian language”) became accepted by much of the Ukrainian-speaking literary class in the Austro-Hungarian Kingdom of Galicia and Lodomeria.[citation needed]
https://en.wikipedia.org/wiki/Ruthenians
[NOTE: This is beyond my knowledge base. I’m just quoting.]
What the Russians claim is as though the US conquered Britain after WWI and now claimed the Brits are Americans. It's ludicrous.