[nathanm412]

It is. OK Google won't unlock a locked phone unless the voice matches, and you specifically enable the feature that allows it to unlock the screen. Once the screen is unlocked however, only certain functions that access your account will need to match your voice (if you spent the time to get Google to recognize your voice.) Performing web or photo searches wouldn't require you to match the voice if the phone was otherwise unlocked.

Asking someone to silence their phone might just be an attempt to get them to unlock their phone before issuing the offending command.