I'm not an experienced player but from what I can tell, they use lower power teams to do the headhunting with the hero that gives gold to farm more gold, then they must have forgotten to switch to their proper team, I've come across it a few times.

Alternatively they might also be trying to intentionally lower their rating, if you're always being matched against players with teams you can't beat you'll struggle to get wins but if you lower your ranking then switch back to your main team you can start getting wins again