I have a couple of thoughts-based on my experience, not medical training.

If the pill did lodge for a while in your throat, it could have caused irritation that lingered after the pill was dissolved. Also, pills are designed to dissolve in your stomach/intestine which would mean that stomach acid is usually part of them dissolving. And there is nothing like that in your esophagus-it is just designed to transport food/liquid not to digest or dissolve. So it might have taken much longer to dissolve than it normally would.

So the long lasting heartburn makes some sense.

Drinking a lot of water before you swallow your pills might help. My Dr has recommended that. You could also try chamomile tea or aloe vera juice. Those are both calming to the stomach so maybe they would help your throat.