How do people know if I snoozed on them in Facebook?

I don’t think so. As far as my experience is concerned, Facebook doesn’t send any notifications to those who have been snoozed by me.

As per Facebook, Snoozing is a feature that allows users to temporarily unfollow someone's posts without unfriending or unfollowing them permanently.

what actually happens, is if you snooze someone on Facebook, their posts will not appear in your News Feed for a specified period (usually 30 days). After the snooze period ends, their posts will reappear in your feed provided you don’t repeat the snoozing period one more time.

Hopefully, the above answer will satisfy the needs of the user.