0-10 in placements gets S4?????

OK so the backstory of this is that a friend of mine is B5, and he played placements with another friend of mine, who had never done ranked before in his life. They literally lost all 10 of their games, and the guy who had never done ranked before ended up getting Silver 4?!?! This just triggers me a bit because in my placements went 4-10 and got Silver 5, which I was pleased with as I didn't want to be bronze, but how does someone who loses all of his placements get placed in Silver 4??? His MMR is 873, which is well within the bounds of Bronze 5 MMR, so why did he get placed literally more than a division above his MMR? Sorry if this seems like a bit of a rant, but I'm just really confused and want some answers :/

EDIT: So I was getting his MMR from op.gg, as that's what I usually trust. Last time I checked, as I said, his MMR was well within the bounds of B5. Now I checked it again recently, and it has gone up to 1264??? He hasn't even played any new games, so wtf is wrong with this system. All of the stats on there have stayed the same too, like his 0.64 KDA :///