This just happened to my phone... I think it was from condensation/moisture when going in and out from shovelling snow.  I never dropped it or got it wet.

Obviously your customer wasn't taking the remote outside (as far as you know) but the moisture/liquid got underneath the outer part of the screen and created the exact same scenario where it always thought the screen was being pressed.  Either way you'll probably have to send it back, and you'll be expecting a bill...