Can someone please explain me this?

Hello guys, im Plat I now and im playing lol for 3 years, and this season, i had a feeling, that my enemy in lane always gets lvls faster then me. I just said that it was just my imagination, but now, i played a Sion vs Cho top, and i got a gank from my ww, we got Cho and i had a assist. Stayed in lane and kept on farming, but Cho teleported back, and after 10 sec got lvl 4 before me, i had it after 2 more cs... so can someone explain to me, how the hell did he get lvl 4 faster than me, even though i was longer in lane, had more cs ( i had 18 ,he 12) and i got an assist and he didnt? And no, he didnt take anything from the jungle, he had no time. Maybe theres a masterie that i dont know, so please, someone enlighten me