Apparently his hangup was he didn't know if pre-Columbian metworlworking had the mastery of heat to anneal metal.
I tried to explain copper anneals at 400 C and liquefies at 1083 C.
Primitive cultures bisque fired pottery at 538 C (modern bisque is 980 C) in a pit. If you can fire your pottery at 538 C and copper melts at 1083 C, you can toss it in the pit and have it come out annealed.