As other said, their not talking about the same obfuscation. If you are interested in code obfuscation and a way to prove that a formally correct obfuscator is impossible, you might want to read a paper called “Can a Program Reverse-Engineer Itself?” [1] I worked on as an undergrad.

The idea is that a correct obfuscator should only obfuscate and not change the program's semantics, which means that it can't change constants that may be displayed to the users, like hardcoded integers and strings. If you use these in a Quine [2] structure to be able to retrieve your original code, then the obfuscator can't do anything: it it breaks the Quine it is not a correct obfuscator, if it doesn't then you can trivially get back the original code. And what is interesting here is that it is possible to take any source code and make a Quine which has it as a payload (it will do the same thing as the original source code except that it will also be a Quine), which is something we had done already for another paper [3].

[1] http://eprint.iacr.org/2011/497

[2] https://en.wikipedia.org/wiki/Quine_%28computing%29

[3] http://eprint.iacr.org/2011/099