Its not against the law if thats what you mean.

These are pop under ads and a very common practice among webmasters. I am not sure its legit way or not, but I am not in the favor of pop under ads.

These are annoying and kill user experience to an extent.

Did you find the website by AdWords? if so, there might be an issue. Moreover, you must remember, that one of the top six most things google hates, is damaging their brand, so if it is pretending to be adsense, this might also be a cause for google-anger. Otherwise...

As you said it not looks like something against law has been done. I think it is okay.

My advise: Check with an attorney or lawyer to have a confirmation if this is legal or not.. or else Hire a professional SEO advisor if you're looking if google likes this kind of pop-up or not, will you have google slap etc.

As you have mentioned in your post you dont own that actual site,why worry about it i would have said that if you had been asking as a result of you owning the site i would have said it is a border line case.This is of course just my opinion.

Thanks guys for your comments, its not my site i just came across it while looking for blogs. Whatever that may be the owner must have found a creative way to earn. Since the submit comment button when clicked will open a new window with an ad on it.

Google is not law lol. It's okay relax.