LSN = low sleep needs. What he's doing at the moment is pretty normal for his age but to go to one nap now would be quite early.
It could be a sleep regression, the rest of his sleep is pretty good though and given he's doing a solid 11hr night, 5am is not an unreasonable time for him to wake. I think its probably more likely that his sleep needs are reducing as they do at LO's get older and if you were to cap that early catnap at 20-30mins, you may have a bit of luck but I think with BT at 6, WU at 5 is reasonable.
Its sensible to keep with the CN and a long nap, so I'd stick with that for now.