Like the title says. Happens randomly now and then.
Game gives me faction I did not select
I've seen this too. I first encountered it after picking ALL the factions, and only getting 1 or 2 of them.
I've since de-selected and re-selected all the factions in each matchmaking queue (1v1, 2v2, 3v3 etc), and it seemed to fix the issue, but it certainly seemed to require said fix.
Of course, it's just 1 data-point, and could totally be random chance, in my case.