I can't speak for the guy, nor for Apple's policies, but I'm let's say 99% sure that nothing shorted during the battery replacement. I did a pretty surgical work. I didn't use any metal tool to pull off the battery contact board or the battery itself, and the screwdrivers are magnetic, so the screws would stay attached to them and wouldn't fall accidentally on the board. Still something unnoticed could have happened. For what I found searching is that there's a batch of early iPhone 5's having some difference in a chip that would stop working when the unit is opened, and the symptoms are like that, the home and sleep buttons would stop working.
Anyway, the SE is a nice device, same size yet faster and with a lot more of room to store music and pics. Today it's going to be the first day using it as the commute music source.