My father encountered a clickbait site a few weeks ago that would spawn pop-unders playing continuous video ads, muted, which closed as soon as they were focuse

My father encountered a clickbait site a few weeks ago that would spawn pop-unders playing continuous video ads, muted, which closed as soon as they were focused. It was bizarre. My only guess was that the site was trying to scam advertisers by "showing" lots of ads to users, without the users actually seeing/hearing them and getting annoyed.