I have only just seen this "crossbow". I have a sneaking suspicion that the nannies here in Australia have not legislated this thing out of existence because no one (here) thought about this, let alone whether it could be done. It's not a crossbow because although it has limbs the force is not elastic. It's not a rifle because there is no expulsion of air or gas driving a round. It can't be an air rifle because although it has something that looks like an air reservoir, it's not one. If it works on vacuum it's not spring powered. I think I'll order one. It will get seized and I will end up fighting customs in the Federal Court but I do court for a living LOL.
For every complex problem, there is a solution that is simple, obvious, and wrong.