I am always wary of players who minraise in spots where they should probably just jam based on stack sizes, especially if they are nitty and even more if they are winning players who should be aware of stack sizes. He could have a marginal hand like an Ax or a mid pair and didn't want to shove and go broke with the CO so short, but this to me seems like a monster. He isn't leaving himself much behind after his flop bet which again makes me wary. He could have 55 here but I definitely would not be shocked to see him show up with AQ/AK/JJ+ here either, since he could have also been trying to induce a jam from you pre. I would have flatted too since you were getting a great price, but his flop bet reads strong, and while you have top pair its tough to really feel comfortable continuing based on how nitty he's played so far.