Even if you use 3D painting software it's best to have a UV layout on top of the texture. My qualified guess is that he used both.

Yeah, it was a bit of both. Started in 3d so I can quickly experiment then when I have something I am more happy with I move to a more traditional 2d approach.

I have started creating a series of workshop tutorials... http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=297595853 from the looks of your workshop you wont need them but here's a link for anyone else. If you like what you see please remember to rate, thanks.