From what I can see of Don Cologne's shirt, it's not a plain Oxford cloth, but what I have seen termed "royal Oxford", which I've seen made RTW with French/double cuffs - a more luxurious version of OC. I think that the shirt is just fine.
I didn't say Don's shirt was formal, nor did I say there was anything wrong about it. I just said it looked odd to me, and I didn't care for it. That is an opinion, not a judgment on whether or not it right or wrong.