It's believable that you could have seen Titanic in theaters and not recognize it. It's a fairly generic looking ship (or maybe underwater lab or something) interior filling with water.
I knew immediately, but despite having seen the film in theaters myself, it was mostly context. Titanic is
by far
the biggest kind of film this could have come from, so the insistence that everyone who was alive then knows was what gave it away.
Like, what other sea films even come close? Jaws doesn't have a ship big enough for this kind of shot. The Abyss or Poseidon Adventure are the only two that come to mind that are even remotely in the same league, and even those are pushing it. Not to mention, if you've seen the Abyss, like, ever, there's no mistaking a scene that well lit as coming from that one.
Arguing on CE be all like:
https://youtu.be/JpRKrs67lOs?si=kPGA2RCKVHTdbVrJ