Ok, your EASY looks quite good, especially because you were out and he was sleeping 2 hours in the buggy. IIWY I would try to have a full A before going out if you know that he is falling asleep, so you know he is not UT - that can also cause NW, but happy ones, not with eyes shut. Just a thought for the future.
It could be habitual, did you used to feed at this time?
You could try W2S - you go in an hour before, so 4AM, you stroke him and see that he stirs, and then leave the room. That suppose to make him start a new sleep cycle. You can have a read about it here:
http://babywhispererforums.com/index.php?topic=213387.0Like I said, I can't see something in your EASY that might cause it, it looks like you are doing great!