I would say "she is here" or "he is here," but not "they is here."
I would say "she is here" or "he is here," but not "they is here."
So using plural form of verbs with singular “they” does not seem that surprising to me.
Likewise, "they" is grammatically plural, regardless of its contextual semantics.
Verb forms agree with the grammatical number of the subject, independent of the semantic number; in English those almost always are the same, but aside from "they", "you" (which is grammatically plural, even though its semantics are sometimes singular) is a case where they can diverge.
That's what I find interesting: that "they" isn't actually being used grammatically as a singular pronoun that can be dropped in to replace "he" or "she." The entire grammatical construct is exactly the same as if "they" was referring to multiple people. It's the context that makes it clear that only a single person is being referred to.