Or did he just read some reviews about how difficult it was?
The game isn't difficult as so much as it is sadistic. No pausing at all, not even when checking inventory. On screen elements that totally block 80% of your screen during battle—effectively making you a sitting duck until it goes away. Remember, no pausing during all this. WTF?! No real story or purpose, so only the masochists will continue to play through if only to prove to themselves that they can beat it. The lack of plot elements mean you really have to rely on the PSN feature of the game whereby players on PSN leave you clues about what to do next. You can kill any NPC, including ones critical to the game such as the girl that levels up your character. It's just a poorly designed game. The whole time I was playing, I was like, "Seriously? WTF?"
However, despite all of its flaws, all the reviewers are right about the game having a strong sense of achievement. There were a lot of comparisons made to the old cartridge days when the only way to beat a game was all the way through in one go. Or where you had to collect more 1-ups to prevent death. Demon's Souls is kind of like that. No save points and if you die, you start back at the beginning of the current level and lose all your unspent money/souls.
Dying in modern games isn't as big of a deal as it used to be. You often start off right where you died with all your items and full stats. A lot of games nowadays have auto-regen health so you just wait it out and you're good as new. Demon's Souls makes player really adverse to death.
And lastly, casual doesn't mean easy or unfulfilling. A game doesn't have to be "difficult" to be challenging. For example, my favourite game is and always will be Tetris. Easy to learn, but challenging to get really good at. I can spend hours trying play the perfect game, get the highest score or see how fast I can play, etc.