Since the continent of Europe straight up assigned the letter W to itself, I think the comment just applied that same logic to Asia and Africa as letters, and then "mate" to Australia to get the full phrase.

It's pointless to have an assumption that the comment was made in ill will. I understand that these days a portion of the US population has those intentions, but I very much doubt many of them are on this platform of all places.

WTF mate. Seriously, WTF mate!