I think it's just a nature of photographers (of all levels) to critically view all photographs, including our own and others, to see if there are any improvements to be made.

Common courtesy should tell individuals, sometimes it is the best to keep those ideas and opinions to themselves. But, that doesn't stop some people. Today, some of us are so used to having opinions about everything and being able to express it without facing any consequences, especially on Internet. I wouldn't be surprised if that behavior bleeds into ones everyday real life.

I'd just ignore it.