seodevse
Found it. In admin;
"Discussion post crawl settings
This is an important setting about crawling your discussion posts in search results."
Disable it and schema will show "DiscussionForumPosting" instead.
Unfortunately headline field is missing.
And it would be really cool if all replies could be included. Don't think its that hard to fix, check how Xenforo done it. The DiscussionForumPosting schema also have a "best answer" feature if I'm not mistaken, just like Reddit has.
Edit: Think image field is set wrong also, mine is set as default favicon. I think that can be skipped altogether on thread urls..
lol how do I fix this myself...