Random skins?

Hello! I'm a kind anew lol player but i own a few champions. i one day choose to play top and choose Jax. i look at the skin feeling sad i don't have $80 to spend on skins but i noticed i had one skin (btw I've never bought a skin). The skin was the mighty Jax which i look up and it said it was limited and only could get during the winter Olympics. i asked all my friends if one of them bought me it (have no idea how reviving a gift works), but they all said no. how did i get this skin? I'm not complaining but was this a glitch or something?