I never played Neverwinter Nights, but single-player games are sometimes designed in ways that appear (and may, in fact, be) not entirely random in order to discourage players from cheating by saving the game and reloading if they don't get the results they want. This is most noticeable in turn-based games like XCOM or Civilization; if you reload a saved game and do the same things you did first time, you will get the same combat results. You can reload your saved game a hundred times, but if you have the same unit move the same way and attack the same enemy unit, the results will be the same each time. It may be that Neverwinter Nights was designed as it was not because of a limitation of computer randomization, but to discourage cheating.
This is an excellent point.
When playing XCOM I noticed that exact same behavior. It's almost as if each move or action has a value assigned to it, is somehow combined with the previous RNG result, and is then used as a new seed.
I agree that single player games are likely to have a completely different philosophy about RNG than an MMO.