Why is my potentiometer giving strange reading?
Unfortunately I cannot comment. I can't really think of a reason why your readings are the way they are. Though you did not present to us an image of what potentiometer you are using and how you are really wring it up.

It is possible that your potentiometer is a center tapped type with 4 pins. You could have possibly connected the positive rail to the center tap pin, ground to the side pin and the wiper pin to the Arduino pin so that you would have the result you are getting.

Or potentially, you wired it correctly except for the fact the positive rail you connected to was 10V, but that is really dangerous.

Have you tried measuring the resistance of the potentiometer from one side pin to the other side pin?