I'd say its way to early to tell. However, bear in mind most young roosters will chase each other around, or spend their time chasing the girls around the pen. While I am not familiar with seramas, the chest bumping sounds more like little ladies establishing their pecking order. Roos get such a bad rap for fighting, when its hens that go at it more than the roos. I have 2 roos, and 11 hens. The hens are the only ones I've ever seen chest bumping, and if the dominant roo isn't there to break it up, they will start flapping and kicking.
My one roo that I raised from a chick with the girls, was notorious as a chick for playing bowling ball. He would look for a pile of chicks huddled together sleeping and run across the brooder straight into them, sending them all scattering. I do remember them chest bumping occasionally, but not the little roo.
I'd still say to early to call, though. Just sit back and enjoy chicken politics. Please pass the popcorn...