No, it is not.
The difference between two numbers is the result of a subtraction. This can be either positive or negative.
The difference of their cubes is 4.
The difference between ANY two numbers that are different, is positive. For example, the difference between -5 and -3 is 2. You can move two whole numbers either up from -5, or down from -3, on the number line.
Not if you subtract a positive number from itself. 3 - 3 = 0
They are 8 and 13.
Formally, the difference between two numbers, x and y, is abs(x - y) which is never negative. If the two numbers are the same then the difference is 0 else it is positive. If you define the difference as x - y then it is positive if x > y, 0 if x = y and negative if x < y.
You get the difference between the sizes of the two numbers without regard for their sign, and the difference has the same sign as the larger of the two original numbers.
0.5 and 1.5
By subtracting a positive number from itself. 3 - 3 = 0