I’ve been trying to figure this out for some time. The messaging around this trailer has been… confused. At best.
Near as I can tell, it’s supposed to be a “live-action” movie within the Toy Story universe. So “Buzz Lightyear” is still a fictional character; he’s not some real guy in-universe, off fighting space battles while Andy’s fucking around with toys or pizzas or whatever. But he’s played by a “real” guy, who could show up in Toy Story XLVII as an old, washed-up actor. (Of course, the toy looks and sounds nothing like him. Maybe they had trouble getting the likeness rights.) And the other characters are played by “real” people, which is why there are so many humans in the movie. Very few space aliens with SAG membership.