Why is it that some players got angry if they loose to a lower rated player and dis agree for a rematch,i believed it is always our choice if we still want to play and we're not being rude to them, what do you think guyz?

There's already been threads beating this topic to death. Do a search for them.

Of course you are correct, but unfortunately some players have fragile egos and/or poor mental health.  Don't get drawn into their anger; send a few compassionate thoughts their way and move on.

1) its always a players choice if they want a rematch (win/loose, higher rating or lower)

2) if someone gets angry and "demands" a rematch then I'll almost always refuse, just because I dont want to play someone who has such a negative mindset.

Does rematch means, the game he just won will be reversed if he lose this rematch?