Don't feel bad. I saw a 12 year old girl outgrapple a teenage boy and grappling wasn't even her forte. Heck, I almost lost a sparring match to a 13 year old girl when I was in my prime because she was just that good. I also almost got chocked out by a girl because she had a flashback during one-step sparring. I had to do the escape "for real" and control the take down in order to keep from passing out.

It's called skill. Martial arts teaches you to use skill to counter physical deficits. That's why you can't always judge a book by its cover when it comes to self defense.

He's more experienced in the art and he proves that technique can beat strength :) stay on his good side and learn from him

Right now is is more skilled than you are. That is common. The individual with more skills normally will do better.

Do u even lift bro?

I'm a decent sized strong teen that can somewhat hold my own while grappling and sparring but when I grapple and spar with the instructor's son, he usually beats me. We are both in kempo/jiujitsu classes and he is a brown belt and 3-4 ranks higher than me. The thing is that I'm 5'10" and 160 and and hes like 12, shorter than me, and definitely not as strong or heavy as me. But then there's other people of higher rank that I can easily beat that are closer to my size.