They're as real as you want them to be.
If you've never heard a koala roar, it sounds sorta like a wild pig. You wouldn't believe that such a huge noise can come from such a small cute cuddly animal - that looks like a teddy bear no less. Albeit with claws.
That said, a friend in the army used to perpetuate the Drop Bear myth to his fellow cadets-in-training, claming they should leave their candy rations at the foot of their tents so the Drop Bears will take those, otherwise they'll take to nibbling on their toes. With full intent of taking the candy himself. :-)
No-one believed him of course.
Till soon afterwards around their campfire sharing more stories, just by sheer luck, a koala accidently falls out of a tree, screams its guts out on the way down, then splashes into the shallow end of the lake they were near. Along with the frustrated grumbling as it dragged itself out of the water back into the bush again.
Cue the cadets scrambling to find their candy, placing them carefully at the foot of their tents...