Have you got a link to a pic? I did a quick google search and he did shoot down an Aussie Wirraway, he mistook it for a zero.

An Aussie pilot in a Spit was once chased by a couple of USN types in Pacific theatre of ww2. They mistook the red dot in the roundel as the Jap rising sun. They dropped their tanks to reach him but he was higher and got away. Afterwards Aussies took the red dot out of the markings! I think it was Bluey truscott? Not sure. Several Poms in BoB shot other Spits down too.

Hmmm, shooting down a kiwi bird would be quite a trick, considering the bird is flightless and about the size of a chicken. ;)

I recall reading that the first RAF Ftr Com battle of WW2 (called the Battle of BArking Creek, I think) involved a squadron of Spitfires attacking a Sqd. of Hurricains mis identified as Me's. Very odd considering that at the time the Luft had no base within about twice the '109s combat range. The Spits shot down two Hurris. The Hurris did properly identify the Spits and didn't shoot back.