Gaming dice

Role-playing is just a style of game. It's like Anime; it can be bad, but it doesn't have to be.

This.

How is it demonic)

Some people think that the magic in DnD is sorcery (which, in often case, they're not wrong).

There is themes associated with it that are demonic. It also talks about a lawless world, which is what the devil wants. I would suggest staying away from it.

time-killer, but also fun

My best friend, who is a Christian, loves fantasy (LOTR, Narnia, etc.) and she's suggested a DND game with me and some of my friends. I fully trust her to not do anything bad as DM; she's one of the most devout Christians I know.
I guess it depends on the Dungeon Master. Roleplay games seem interesting as long as they are organized well.

Yeah, DND is not demonic lol. The only way I can see it being demonic is if they start actually trying to chant spells in the game or something like that.