I'm only on the free trial, so I don't want to waste my free searches trying to figure out how large of a problem this is, but a lot of the results when I turn on the forum option are not from forums. My query was something about how to make sure your veins are large and full enough for blood donation, but I got things like this url for a pdf that doesn't seem relevant and isn't attached to a forum (maybe project muse has a forum somewhere, but this isn't what I'd think people are looking for when they do a forum search). https://muse.jhu.edu/pub/176/oa_monograph/chapter/140452
Another example was an uptodate.com page. I don't think they have a forum, but even if they do, the url in my search results wasn't a forum page.
I only expect forum pages when I toggle the forum option.