I think two things are being communicated with "actor"

1. Unlike traditional animation, these AI characters are being "directed" in a sense that's unlike traditional drawing frame by frame.

2. The broader question of relationships that people are forming with AI, whether that's chatbots or AI influencers or the weird hologram Girls In a Jar stuff or whatever else.

That's not to say that actor is the right term. I think some of this is in "is a hot dog a sandwich" territory. But I think that's what people are trying to say with their use of the term.

And animated characters doing all kinds of acting or modeling jobs isn't exactly new.