Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

The Lizard chieftain failed a save against a mass blindness-deafness, no message was displayed about some kind of immunity, still he was able to cast and attack.

What it do?

Some bosses and probably some mobs have their own 'skin' . there was one time the 5 headed hydra was dropping the skin in Yuan Ti temple.

ex:
skin - immunity to knockdown
skin - immunity to death spell etc

that can be picked up by players. the bug was fixed and the skin was removed from players who picked it up though.

Lizard Chieftain might have immunity to Blindness skin.

There should be a message in the combat log about an immunity if that was the case. He also got the icon of being under the effects of blindness once he failed the save

he is a barbarian tho, any spells he has are not normal and may bypass those restrictions because of that

Looking at the screenshots, it looks like he had a 50% miss chance, which is indicative of being blinded.
Your spell most likely worked properly, and he probably doesn't have any immunities.

IIRC, the Blinded status gives a 50% melee miss-chance and prevents ranged attacks, while Deafened gives a 20% miscast chance for verbal spells.
Neither should outright prevent melee attacks or spellcasting, if that was the question.

[Addendum] Here's the Wikia source on said statuses:
https://nwn2.fandom.com/wiki/Blinded
https://nwn2.fandom.com/wiki/Deafened

There were 3 other enemies - 2 warriors and a caster. Only the chieftain had this behavior ie casting a spell directly on my char and attacking. Anyway this sounds legit. Everything is Gucci