Upperdark Creature Issues

[Valefort]

They rolled 20 which means they'll hit you, no matter what, even if you have 1000 AC and a tiny kobold rolls a 20, he'll pierce your AC

http://nwn2.wikia.com/wiki/Natural_20

[Camera9]

Eheheh I had the same confusion when I first started playing this game ^^
Of course they hit me but it's not a critical hit until you confirm it! If you're not able to overcome the AC that will be just a normal hit, not a critical ;D
I can hit a dragon at level 1 with a 20 but I will still need a double 20 to crit it!