What could be the reason?

There's this guy I've been talking to on a dating app for few days and he said about meeting up and I said won't be for a few weeks unfortunately because I've got work and events coming up he said it was fine and he wouldn't mind waiting he seemed proper interested yesterday asking me how im doing and what I'm upto and now not replying for hours which I don't mind but before he'd reply quickly and ask me questions now its one word answers when I try to engage should I ask him or just move on?
What could be the reason?
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