Or one of our subs had been following him and then started to “actively” ping him as if getting ready to fire. The chicoms then got scared and thought they were about to be sunk.
Maybe him surfacing was a way of saying “unc-ral, so sorry”. When he new the jig was up.
At least that is the way I hope it went down.
Our sub wouldn't have for the same reason, you don't tell your opponent that you've been tracking him.