$75 to win $250 IP is a more than reasonable price to continue. Without some knowledge of V I'm not shoving here as players rarely c/r and then fold. We block a lot of flush draws so he is more likely to have a value hand. He's also not c/f his hand when a diamond comes so we have implied odds.
Tough one as the confusion could be a tell. If we flat and he jams a brick turn? Really no reads? No level of activity to measure? No impression of confidence or competence? Did you ask him how many jacks are in this deck?
What others said - to the extent Aces or Kings are outs for us, we won't get paid by worse if we flat the flop bet and one of those cards hits the turn. Plus folding to a bet from him on a turn blank feels filthy. Even more plus, most of his range will c/f on a diamond turn.