There's two things going on there.
First, Jungle Grub only exists in Uncommon rarity at the moment. Same goes for Clouded Hedgehog and Silent Hedgehog. You can verify this with Warla's nifty list
The second thing is that pet spawns can be linked, in the sense that all of the Kuitan Mongooses within an area will be the same rarity and have the same additional pets come with them (also with the same rarities). This is especially noticeable in Pandaria zones.