Well, what I've seen is check-minraises getting folds (as well as calls of course). And tbh in this case I did also consider if I was just behind (a higher pair for instance) and should fold on the flop when he check-raised. I cannot speak to what his expectation is, but it seems not entirely unlikely that he considered a fold a possible result of his check-raise. You're right about people being generally honest about their bet sizing - small for when they want to be called (and are strong), large for when they don't want callers (and are weak) - but it's not impossible that others have made the same observation and adjusted.

I'm reading his check-raise to suggest that he doesn't believe my cbet signals strength - and that he is strong relative to the flop.