Hand...

I like your point on the turn, AK does not seem likely to check there. It is HU, so maybe villain is playing a little strange and was hoping you had a worse A? If I were villain and had AK and somehow checked the turn, I just don't think I would check the river. I don't know what hands would be a good fit for a river c/r, it's not like you've shown a lot of aggression here.

Then again, as somethingclever states, it could be someone thinking they are being tricky and I'm over thinking it and missing out on value.