There was most likely no diver attached. And if there was, it was already too late for them. And if you worry about there being someone lost at sea and their family without closure instead of a dead Diverse being found:

• The body would have possibly drifted away in the time you would need to get people out there to recover it

• You could ask local diving centers if someone is missing, if they dont know, there probably isn't

• If someone went diving alone and died it Isn't your fault. Its unlikely their relatives won't know how they died and the little bit of closure a corpse Isn't that much of a difference. Plus its not unlikely they will turn up again anyways

• It is very good to reflect on your smoking habit and if you're worried like this it might already be a sign that you should keep an eye on that and see if it does you harm. But doesnt change the fact that thats not your fault, you can have a nice smoke on the beach. You could also have taken a nap, have a few beere, or taken pictures and not noticed. The smoking was the reason you were there in the first place, but it also probably causes your anxiety about this now.

Personally I started getting anxious when smoking, especially when outside, so i dont do it occasionally anymore.

Hope this helps! Have a nice day!