Moving between leagues

Hi All. Not sure if this belongs in here but then I’m not really sure if it’s a bug to put it in there. 

I’m currently Master League III and yesterday got a challenge match against someone in Tiberium League. I expected to get wiped out but won - opponent had a deck a decent bit less developed than mine so I assumed they were just trying out different units that they’ve not really advanced fully yet. But no, their whole collection was quite lightweight for someone at Tiberium level. Fair enough I thought, they must be pretty skilful. Then I looked at the game history and it’s really weird so wondered if someone could explain what’s going on to me. 

I’m guessing they’re at the bottom of Tiberium League so can’t drop out - but then at random points in the game history they show up as Master League III, then after one victory jump back to Tiberium League. They don’t go progressively backwards i.e. Master I, Master II then Master III but seem to shift straight out of Tiberium and back again. Is there some weird tactic going on here?

Thanks for any insights. I’ve attached three screenshots taken across yesterday and today to show what I mean (my win is as Pappjikov FYI).