Eh, I feel like this probably occurred in the sort of place where you implicitly consent to touching subject to body language. The initial grinding would be considered an “unless told not to” type of thing, and then when OOP “went with it” that was consent for a little more and so on. Verbal consent is the gold standard, sure, but some people like to read and be read between the lines. After all, OP and OOP both seem fine with the situation.