Every post has comments that haven't read the article and then go on to give an explanation that they assume the article lacks.

It somehow feels like the HN equivalent of mansplaining.

I agree, it's a bit annoying.

But, in my opinion, in this particular instance it could be seen as a meta comment that the submission title is wrong. It says "submarine", but the vessel in question is not in fact a submarine and that is also annoying.

The title is supposedly written by someone who has read the article they're submitting, after all.