"a bag of salt water, which is what a cell is"!!? Wow. It always amazes me how physicists manage to reduce the extremely complex and beautiful world of biology for their own computational comfort. Is your brain simply a "bag full of bags of saltwater"? The SAR test rationale assumes it is.
No, the ocean blocks radio waves because its index of refraction at RF is very different from that of free space, resulting in a massive impedance mismatch at the boundary. In bulk matter, this is a scale-independent phenomenon.
There's actually a lot more to the question than size. RF is all about boundary conditions, and everything else is a consequence of that fact. It's a fascinating area of study, and in all seriousness, I'd recommend you take a look at some of the underlying principles behind EM physics and propagation. It'll help you reject "not even wrong" bullshit like what's portrayed in this article, and even better, it'll give you a deeper appreciation for the way wireless technology actually works.