Backlight turning on randomly but turned totally off in settings (7S SS 8.37)

I did my first long night run on Friday night in preparation for a 100k in 4 weeks.   I noticed the backlight kept coming on while I was running.

I checked my settings and buttons and touch for backlight were enabled, wrist gesture was off.  Touch also disabled during activity. So with these settings the backlight should only come on if I press a button.  But, seemingly at random, the backlight was coming on on its own.

I changed settings to backlight off and it still displayed this behaviour.  Has anyone else noticed something similar?

I was using course navigation at the time but it didn't seem related to off course notification or anything to do with the course nav.