I recently purchased a non-Nest smoke alarm. The documentation explained that if there was an alarm, the hush button would silence it temporarily, but if there was a high level of smoke, the hush button would not work and the alarm would not be able to be silenced.

Since both Nest and other smoke alarm companies say this, I conclude there is some regulation to this effect.

The Nest device in the video did not appear to be experiencing high levels of smoke.