The "redefining keywords" is the pre-processor. That's what it does. There isn't anything magic here. Strictly speaking it can be run entirely ahead of the C/C++ compiler, on any file you want. There's no requirement that it is C/C++ - you could use it on a python script (as long as you weren't using # comments anywhere :D )
1. Not easily distinguished
2. Not readily understandable/expressable
3. Not commonly known
I didn't see the author use the word "bizarro" anywhere, nor make any claims about any of this stuff being weird. He actually presented almost everything in a fairly neutral tone, except when he said that using the preprocessor to override keywords was dangerous (which could be construed as opinion).
I'd say that a feature of C++ is still a feature of C++ even if the same feature is in C.
For example, I could do:
class MyClass {int operator+(int a) { return a; }};
MyClass x;
x + 1; // Valid.
1 + x; // Type error.
= -> [] ()