Night Light turns on 1 hour earlier when set to automatic

Night Light is set on auto - "Sunset to Sunrise". My time zone is correctly set to EET (+0200). According to this site - https://www.timeanddate.com/sun/bulgaria/sofia - the sunset on December 28th occurs at 17:00 local time (15:00 UTC). The night light activated at 16:00 (14:00 UTC).

Either I don't understand something, or this is a bug.