Where are you getting this from? I don't see anything anywhere online or in the trailer that confirms it's an exclusive... considering it was announced as a multiplatform for PS4, XBO and PC and as far as I can tell nothing has been said other than it's coming to PS5 now.
There are a few articles that speculate it might have some exclusivity even if it's just launch.
There was also a thread in either GAF or ERA speak about it. The CEO buying all the Devs a PS5 for the trailer might even further strengthen the arguement.