i don’t think it was so inexplicable - carson did not hear his cue, and then when the guy backstage was telling him to go out, he was like “hey, they didn’t call me, why do you want me to go out there?”. i think trump did not hear his name either. trump probably thought (as carson did) that they changed the order they were supposed to go out on the fly. i think one of the two commented on that when they finally made it to the podium.
basically this is on the show organizers, but it was completely hilarious.