The question is not whether BCrypt is backed by Blowfish, the question is whether BCrypt uses Blowfish in a way which is cryptographically sound. If it does not, then an attacker may not need to use brute force. Assuming the author has read more of Mr. Schneier's book than the quoted preamble, he should know this -- Schneier discusses this at length in both editions of Applied Cryptography.

Again, an example of this is the 3DES encrypt/decrypt/encrypt process vs. a more naive encrypt/encrypt/encrypt process. One is substantially stronger than the other. One is a secure way to use DES, and one is not.