Why am i strong but still skinny?

I am a tad over 5'11" and weigh about 180 lbs. Although i've never weighed this much before i still look really skinny. I have a pretty low body fat percentage so maybe thats why but you would think id look more muscular. Anyway, my physique isn't even as good as it used to be yet i am much stronger than i used to be. I also noticed i am as strong as guys much bigger than me.