As they should be. How anyone is this dumb in 2019 is beyond me. How hard is it just to not make a racist gesture.
It's obviously because they don't think it's a racist gesture. There aren't many asians in Argentina, they probably haven't had contact with many of them or know very little about their culture and what would be considered offensive for them. It's different in countries like Canada, the US or western Europe where racism is a very sensitive issue due to the plurality of races/cultures living together. The average citizen in those countries is much more informed about the matter.
And I know Conte played in China, but he could barely communicate with anyone while he was there, so I doubt he had the opportunity to learn anything about racism in asian culture.