How do sprinters have a tough upper body?

I see varsity cross country kids compared to the varsity sprinters, the sprinters look like they lift weights and do all of this stuff, they have a really fit body, which is what i want to achieve, and the cross country guys are skinnier. I asked a friend who has a reallly fit body and even big arms and such, pretty much really cut and fit, and he said he just runs 400m, then takes a 2 min break, then 300m.. 2 min break.. 200m.. 2min break. 100m.. every day, I don't see how that gives him upper body muscle, he said it just does. I'm confused?