Over 103 hands...

Has he made a river overshove previously? Have you called a river overshove without the nuts previously? Has he seen you tank fold to an overshove previously?

I feel like when I see these kind of bets, villain is saying one of two things...
a) I have the nuts,
b) you're only calling the nuts.

If he has a really solid read that you're folding non-nut hands, well he could be doing this with the nut blocker Ah.

We're talking about a 26/23 here... solid stats, he's very probably playing the HUD game and referring to his notes.

Either he thinks you're not capable of folding big hands, or he thinks you are. Which is it? There's your decision.