Why random player can find diamon and lv 6 in same game ( I'm lv 24 and this is my aother ID ).

I'm lv 24 ( this is my another ID in Thailand that bronze ). In the morning but random system find lv 6 to played with me and that game his score is 0/10/7, and my team in same game had diamond he played very good but I don't understand why I can played with him that I 'm lv 24 and solo q but is I play with my friend that lv 30 and have mastery lv7 3champ and sometime I played with platinum that I understand why I can play with platinum because my friend have mastery lv7 3cham, but this is solo q and play with diamond and lv 6 in the same game. In the night I find lv 30 but so stupid he played Nunu sup and his score is 3/12/17 and he don't have any mastery lv5, 6 or 7 what is this mean he is in bronze2, I understand why I can play with him because it 6 lv far. But he so stupid than he can stay in bronze 2 and this is new year I can play 3 game and all of 3 game I lose because team are feed and stupid.