@Deks answered that. Also Trills are two lifeforms. The AI might have sensed the symbiont. We know Grey is special and not the usual past Trill host. What should occur? They removed him from the dilithium world and cut him off from the subspace connection. The dilithium wasn't keeping him alive. The holodeck was. Why not? The holo worked for 100 years and the two techs are related. Michael is related to Spock who is revered by the folks on Ni'Var. Saru and Michael established a friendship/connection with the Ni'Var, especially the leader in Saru's case. An entire episode was devoted to this. It's not out of the blue. Gabrielle Burnham has lived among the Ni'Var for a year or more. I think she's up to date. She didn't live in a vacuum all that time. The trope is a relative suddenly appearing, shocking a main character (usually causing drama) That's what happen with Sarek, Kyle Riker and Gabrielle Burnham. So it's exactly the same thing. How they "arrive" is irrelevant. I only got so much time and this is an active board. '