Edit: It is a bug, to get one you need to do your level 50 class quest and you can buy the tabard from the vendor in org, I highly doubt when this bug is fixed it wont be removed, though.
I ran Slave Pens on my Warrior today....and the healer had on a....Blood knight's tabard? he was a goblin shammy...I didn't think that it was possible for classes other than pally to get it....
Since I know some will say "Screenshots or it didn't happen"
Anyone have any insight on this?
Can other classes somehow get this or is this a bug?
When I asked him about it, he responded " I got it in org for nothing "
Not particularly helpful, but there ya go.