He was playing against diamond/master players. If it was Rich + 4 bronze against 5 bronze, he would carry most of the matches for sure.
It’s just luck to be honest (or bad luck). I’d also recommend not looking at others profile unless it’s to look if they play some role and they can fill if needed, because you really don’t want to leave something like healer to the last pick and then he has none. But never look at winrates or match history, most of the time it will just tilt you before the match even started (even if you don’t notice it). I won several games with people that had pretty bad loss streaks (20+).