Yes, I'm aware that until perhaps the early 20th century, "liberal" meant essentially what "libertarian" means today.
You're correct that the word "liberal" was co-opted in the early 20th century to refer to the left. I'm not so sure how much that change in the semantics was from the left itself, or how much the change came about as a result of political commentators of the era.
Well the UK Liberal party started up with what they called “social liberalism”, what they called building a welfare state, in the late 19th century and early 20th century. It’s probably all their fault.
There are still “Liberal” parties that aren’t socialist in some places. The Australia Liberal Party and the Liberal Democrats of Japan are the main center-right parties in their nations. The Free Democrats of Germany are basically libertarian.