Did he keep talking about it? I thought I remembered that he got the hint immediately and clammed up ... even though that would be a little unusual for S1 Data.
Directed to the OP: Who's supposed to have abused whom, anyway?
Agruably Data since he took advantage of someone who was not in a state of mind to give consent at the time of their encounter. Though at that point it may have been early enough in the events for Data to not know Tasha wasn't in her right mind and, as I said, once touched Data no longer was in his right mind either as he was also vulnerable to the Psi 2000 virus variant.