Certainly, I didn't mean to imply it is, just use it as a benchmark against which you can get an idea about what the 84 is actually capable of (the Portal thing isn't really a great demonstration of that).
(It is not in fact even a 3d engine, but rather a vector BSP 2.5D one that is technically similar to Doom. To the extent with Doom has physics (pretty much only momentum (seen prominently in how explosion knock back effects entities) and gravity, so not really) that demo kind of has physics. Actually I don't think he actually does momentum, and his gravity is primitive. He's pushing the calculator pretty hard, I'm not sure how much more you could add, but the 89 can do much better.)
Not bad but it is not a 3D Physics engine. Just a renderer. Not the same thing. Still pretty impressive.