It means roleplay is mandatory, so it's not a game for you if you just want to play alone by yourself, you need to roleplay with other players.
Roleplay means acting as your created character would and speak like your character would, so not speaking like this "LOL BROOO HOW U DOING?" but for example if your character is a polite human they may speak like this "Greetings good sir, how is your day?"
If they are an angry orc they may speak like this instead "Meh smash yoo puny oomie!"
I know the feeling as I experienced that hostility in neverwinter nights servers, but Illarion's community is very friendly and welcoming to new players, even our 1 evil player is on break teaching the game to newcomers!
of course it isn't the point, and i try to rp as much as possible in games like this, but sometimes you just need to talk tactics or get someone to do a quest with you. outright banning it seems counterproductive.
I think tactics can pretty easily be done while rping. They mostly want you not to use modern terms and follow the personality of your character as far as I can tell