The earlier wake-ups could be a sign that OT is creeping in a little bit, but that's not surprising if you're getting short naps too. I would probably continue to reassure him as needed and then work on sleep training once he's caught up a little on his sleep. What is his mood on waking up in the morning?
It may be he is self regulating a bit by shortening his night and perhaps needs a bit of a shorter nap. But, it could be a developmental blip. What is your instinct at the moment?