[Xizor]

I do not have much experience and I don't think I have ever seen a move like that before.

1) He could have AA and have overlooked the first limper.
2) He could have something crappy and just wanted to take it down.

I really don't know - I think, however, that you should bet the turn, on the river you might just have given Ax(K?) a free chance to suck out on you.