especially considering they actually have inputs for suggesting a website and signing up for their newsletter (that can't be filled out)

Good for the site engagement metrics

Is that a known intentional dark-pattern to drive engagement?

In this case, Hanlon's razor almost certainly applies. In terms of engagement, if someone wants to subscribe, that's better for engagement than infinite scroll.

A pretty unconventional way to prevent more than 1000 submissions, I guess.