Financial. There is no way (within the realm of reality) that they could provide enough space to someone intentionally trying to abuse it. They stake their claim that since not everyone is going to utilize their allocation in full it's therefore unlimited which it's not, just more than sufficient. It's all in the semantics of the word. They don't actually mean "unlimited", which is the point this guy is trying to make.
And as fast as they could throw more storage onto their network, a properly designed script or program could fill the space forcing them to perpetually add more storage which at some point they will not do, which would prove his point that they lied. If they were willing to keep throwing storage up as fast as they could with no regard for financial loss, then I'd be OK with the claim, but I doubt that's the case.