Seeing that everything stopped at once, I'd bet that is exactly what happened.

Shades of the Thresher disaster. No doubt we'll hear a few months down the track that the Navy's sound receivers did actually pick up the implosion noise.

or someone makes a startup offering submarine exploration of the titanic tours crash site

Recursive Ventures

There was some speculation that any sort of implosion would've been detected by military sonar, and it hasn't been yet. I do not know if that's accurate -- just repeating what I've heard.

doesn't necessarily mean they ever tell anyone about it, it would just reveal capabilities.

Ah, I didn’t see that they had emergency resurfacing methods. I don’t have much hope for these guys.