I just think it's kinda funny how anyone can say without hesitation that a uniform is this or that. My point is, that many coats or jackets look similar and it is impossible to say - with conviction - that it is one thing or the other. Based off the OP and later remarks by Bloody7th, it was more than likely a Confederate early war model frock that closely resembled the Federal issue at the time.
Bloody7th, I believe it is an early war Confederate frock. But, we can't say for sure. Your story makes sense. Plus, the guy looks to be in good health and had not yet suffered the exposure of camp and field life yet. He seems to almost have a slight smirk on his face.