Ok, so I just beat inFamous and for some reason I unlocked the Hard Finish trophy. However when I started playing the game I was sure the it was on the default difficulty, which is normal. After I unlocked the trophy and regained control of Cole I paused the game and noticed that my difficulty was set to HARD. I never changed the difficulty and the game seemed so easy, which makes me think that somehow it glitched up. DId this happen to anyone else?

Strangely enough, this happened to me in Dragon Age.  I know I was playing on normal for most of the game.  Then I started noticing that Morrigan's cone of fire thing (I can't remember the name at the moment >_< ) was doing some minor damage to my tank.  Turns out, the game had been on hard for quite awhile.  No idea how it happened.  
 
To get back to your question.  I don't know what caused it, but hard on inFamous isn't painful or unbearable by any means.  If you accidentally started the game on hard and had nothing to compare it to, you'd probably just think that it was a somewhat challenging game on normal mode.

The game sets the diff automatically after the first mission. You might have missed the sign. 
 
The game is not hard. Some of the side missions can be troublesome, but I finished it twice in Hard for each ending, and it was not hard.

" The game sets the diff automatically after the first mission. You might have missed the sign.   The game is not hard. Some of the side missions can be troublesome, but I finished it twice in Hard for each ending, and it was not hard. "

^^^ I can't seem to be able to reply to your message. Either site is doing maintenance or safari is messing up. Anyways was the comment directed towards me or EvilTwin and if it was towards me is there a certain criteria for the difficulty it recommends or what?