Neither really. I doubt an A-League club would be turned into any sort of ethnic club unless we get pro/rel. It would defeat the purpose of having the A-League which was created to stop the NSL era racism and violence that plagued the game and gave it a "wogball" image.
As for the prejudice part, I think his concern's were more about the ethnic violence and stuff rather than the specific nationality (in this case Greek). I personally think the ethnic clubs have some awesome culture and the food stalls cook up some great food, overall the ethnic theme is quite cool, but I don't like the racism or ethnic tensions that come along with it.
On Reddit the opinion seems to be that Championship/NPL clubs (especially the big Croatian clubs like Melbourne Knights and Sydney United due to their Ustaše supporter groups) have a bunch of racist right-wing Ethnic fans who ruin the image of Aussie soccer. In reality it's a minority of fans that cause fights or are racist, but that's still a big problem (especially since they're loud and have big groups on Facebook, the boomers' favourite site).