Popped a power supply fuse - What did I do wrong?
I would think that most likely the power supply was simply faulty when you got it. Second most likely is that you dropped some conductive detritus into the power supply while you were working on it.


  that looks similar to this


The words "looked similar to" are setting off alarm bells here, if you bought a power supply from a reputable vendor you should be able to give us a link or a part number or something! So I would guess you bought this from a less than reputable source.


  After stripping it, I noticed that there were three wires, each a different color:
  
  Green (I assumed this to be ground)
     White (I assumed this to be neutral)
     Black (I assumed this to be live)


That would be the normal american color code. Even if the colors were somehow wrong it would not have resulted in blowing the fuse in an otherwise disconnected power supply (it may have resulted in you getting an electric shock but that is another story).


  Did the copper of both the neutral and ground wires being close together cause it to arc, resulting in a short?


A short between neutral and ground is likely to trip a GFCI, but if the installation is otherwise normal it's unlikely to do much beyond that. Even if by some stroke of bad luck live and neutral connections were reversed the fault current would have flowed OUTSIDE the power supply, so it would have had no affect on a fuse INSIDE the power supply.

P.S. I usually use insulated ring crimps on power supplies like these. I find they give a secure result and make the connections more touch-resistant than they would be if bare wires are used (though still far from touch-proof, a power supply like this should be inside an enclosure).