You're confusing MP3 bitrate measures in kilo bits per second (kbps) with sound sampling frequency measured in kilo hertz (khz). MP3 bitrate controls the amount of data compression of the original audio. Most music available in MP3 is compressed at least at 128 kbps to sound similar to CD quality, 64 kbps usually always has a noticable loss. Kilo kertz is how many different sounds are played in 1 second. Audio on a standard telephone is 8 khz, CD audio is at 44 khz. The Kate voice both in the MP3 and in real time make 16000 sounds per second, or 16 khz.
The demo on the page is a recording of the 16 khz Kate voice in a compressed MP3 file at 64 kbps. If anything, the compressed mp3 sounds worse then the real thing, as the compression reduces audio quality.