Ya, custom loop for forums:
It doesn’ t look like Andy has documented this yet but there is a group forum loop just like other parts of bp have a loop. Look at bp_has_topics() in bp-forums-templatetags.php. It looks like I’d use that if I were you.
See: https://codex.buddypress.org/developer-docs/custom-buddypress-loops/ for examples using other bp_has_[something]() loops.
That might be the best way to go with this.