If I recall correctly, Wights, being Light Sensitive, did have disadvantage on attacks while being exposed to a light source. At least regular Wights of Bone Keep in game version 2.6.0. But now in 3.3.0 a Wigth in a random encounter and that special named Wigth outside of Bone Keep both didn't have disadvantage.
The tooltip seems like it's meant to be of a certain kind of Soraks, so either those Wights learned it from friends, or it's a bug.
P.S.: the log on the last pic says the Wight attacks with disadvantage - that's because of Faolan being under Protection from Good and Evil spell, not because of Light Sensitivity.