Turns out the number of websites listing former Cents forward Dustin Johnson with Canberra Knights (AIHL) are incorrect.
I sent a note to Johnson myself and got this response:
"hey Brian sorry but there has been a misunderstanding I'm not playing in Australia, I'm in Penticton haha."
I'm not sure if there's another player out there named Dustin Johnson who is playing in the Australian Ice Hockey League, but my guess is that there's no record online of this player and the websites listing the Dustin Johnson who played for the Centennials just assumed it was him.
Sorry for any confusion!