I do have a general understanding of AC, but I guess what I'm not understanding is how the current leaks through with the hot and neutral swapped even if it's a single pole switch. How is the circuit complete and allowing electrons to pass if the switch is open? Are you saying it's trickling through the ground?
I'm not saying that you're wrong, and that in your case it wasn't a real issue, but I do stand by my previous statement that not all timers are made for LED fixtures, and that making sure that your timer is rated for LEDs should prolly be at the top of your checklist.
Certainly it's possible to easily wire AC backwards, and not realize, but I would hope that any certified electrician would wire a house properly in the first place. As
@1212ham pointed out a $5 outlet tester will give the quick answer on that piece, and is certainly worth the $5 investment to add that tool to your kit, if you don't already have one.