the SSP type could have been bottom limited where you pretty much stick out like a sore thumb even at slow speeds over distance and there isn't a layer to attenuate your noise emissions.
Judging by your keel, I'd think you had bottom limited SSP and no layer present.
the attack could have been the initial reaction (snapshot) from AI once you were detected, yet AI didn't have a good solution on your location.
the contact could have been in your TA baffles, which is why you couldn't see him initially. However, if you got a TIW and the contact is a torpedo that can only be fired from internal tubes(wire-guided torps) then that gives you some data to consider.
