A question about matchmaking

Today i duo queued with one of my friends for a few games and completed my promo series to Silver 2. My friend was in his promos too but he needed one more win to rank up to S4. The next game we also had a teammate that was playing his first promo game to S2. The fourth teammate was S2 as well. Here comes the interesting part. That game we had a Jax jungle that was in his placements. Not his promos but his placement matches. On his account there is 1 single ranked win and 4 other games he played he lost. Even the game that somehow his team won he went 3/11 Ashe adc.

He finished in 4/19 Starting the game with simply being bad and feeding his ass off then proceeding to stay afk in the base. When we told him that he is single handedly losing the game he ran down mid a few times and stayed afk. How is it that we have two players in his promos two players in Silver 2 and recieve a teammate that has not even recieved a rank yet and even in his brief history of playing he was always the one to feed.

I simply cannot understand how this can occur. I wouldn't give this too much attention but we had 2 guys in promos which are quite important games. Also if the guy needs teammates to play with why isn't he matched with bronze players where he (maybe) won't feed his ass off for the sixth ranked game in a row?