Last time I used a Qu-16, the channel mute and mute group states were independent (1.9 firmware). The closest way to unmute just one channel would be turning on the mute group, then turning on the regular mute for each of those channels; turn off the mute group again and any channels you didn’t also mute independently will be unmuted. Bit of a hassle though.
I think when I was looking at the manual a few days ago I saw a line that mentioned short/long blinks of the mute button indicating if it was just muted from the mute group, or also muted independently.
Edit: On page 44 of the manual it says “A short flash shows it is muted by the group only. A long flash shows it is muted by its Mute key and a Mute or DCA group.”