Have you made any attempts at lengthening his naps? Can you give us an idea of his routine, even though it is broken by short naps?
He will surely continue with this early bedtime until he takes longer naps. I don't think it's "wrong," but it's probably difficult for you, or at least it would be should you have evening plans.
It just looks like he's starting his night time sleep a little too early. If you could manange to shift him forward in 15 min blocks, it may even out a bit. Say, bedtime at 5:30, then 5:45, then 6:00, etc. To do this, you will have to work on lengthening his daytime naps so that he can make it till a later bedtime. Do you ever treat the 4:30/5 sleep as a nap and wake him? He may have a hard time with it in the short run, but in the long run, it may get his sleep sorted out.