Why doesn’t dictation work on GBoard in incognito mode?

My impression was that GBoard dictation works completely locally.

https://ai.googleblog.com/2019/03/an-all-neural-on-device-speech.html

If that’s the case, how come it does not work when I go incognito on Chrome? It crosses out the microphone icon in the top right of the keyboard. Did they just forget to disable that feature after they made it work offline?