No, he's saying you compress CBR, then encrypt. Not compress CBR -> gzip -> encrypt or something silly like that.
CBR audio codec, then encrypt gives you a constant-bitrate stream indistinguishable from randomness. That's pretty much the gold standard.
(Of course, that still only encrypts content, not metadata. You can encrypt a phone call in such a way that a watcher gets mathematically zero information about what's being said, but the watcher still sees who is calling whom, when, and for how long. Hiding that is much harder.)
CBR audio codec, then encrypt gives you a constant-bitrate stream indistinguishable from randomness. That's pretty much the gold standard.
(Of course, that still only encrypts content, not metadata. You can encrypt a phone call in such a way that a watcher gets mathematically zero information about what's being said, but the watcher still sees who is calling whom, when, and for how long. Hiding that is much harder.)