Who you attack is based on...?

Sorry if this has been posted before anywhere else but I wasn't able to find anything on it.

I was just wondering if the people the game selects for you to attack is based on your trophies or your level? A friend and I just started and he's level 9 (About 2 days of playing) and he's getting attacked by people with like 8 giants, yet when he's looking to attack he can't find anyone near his level anymore.

Thanks for your help.

It is based on trophies which I find dumb. It should be based on level, but no, they encourage farming.

its based on trophies, if it was based on TH lvl or something, I could get to champion with no problemo