When did the first homo sapiens exist? Ideas like species evolve. Saying there are no original ideas seems to me an attempt to glibly capture something quite fundamental.

I don't disagree with your premise, but I'd argue that saying "there are no original ideas" in the context of a discussion of plagiarism is needlessly reductive. Even though I think I mostly agree with the author here, I think there are legitimate counterarguments that can be made; equating all of the ways someone can cite or build upon an idea with copying something word-for-word and claiming it's your own is not one of them though.