Is it normal for a teen to have musles without lifting?

ok you see i graduated from highschool i had friends i wasnt that popular i was bullied cuz i was very week extremly week i was bout 5 feet 10, NOW im 18 the same age and im ripped i mean i cpnfronted my bully from highschool and whiped his ***... how this happend i nvr lift i dont run i dont do excersise... i was bout 165 pounnds wen i was bullies. now im 180 pounds, i nvr grew but how i get so ripped its a mystery