One of the factors of placements is where you placed last season. He might've been lets say silver 5, you were bronze 4 or something. His mmr was higher last season so this season as a result he gets a bit higher placement.
When in the 10 runs you get your wins also matters. If you lose your first 7 games, then win 3 in a row, your mmr is basically trash compared to if it was the opposite. The games at the beginning stages of the run matter a lot more than the ones at the end.
And as others have said, bronze 5/4 is nowhere near rather well. Not trying to flame here or anything, but you obviously can improve how you play tremendously. My advice is to see where you can improve and hopefully you will climb to an elo you can be happy about, or improve so next season you will get placed where you want to be.
This isn't a glitch though, there is a specific reason behind why you were placed lower than your friend, whether it be where you lost in your series, your rank from last season, or the players you were matched against. The elo system is random and while nobody but Riot knows the exact formula for it, it exists.