2 possibilities here:

1. They've had it all for a long time, but haven't rounded everyone up yet because they've been waiting on the great public awakening so that when they move, the evidence they have on them is already largely known and the pushback from the public will be virtually non-existent.

2. They didn't have it, but thanks to the Quantum AI they used to see the future (Project Looking Glass) they knew they would have it, and when and where they would get it. So Trump stated confidently that something had happened that hadn't actually happened yet, the same way Q has apparently been doing this entire time (future proves past).

Either way, the outcome is the same. Just a fun trippy mind-game to play cause why not.