He is using both digits and the nubers that sequence of digits represents in that equation.
In base 10, 7641 - 1467 = 6174.
In base 11, 7641 - 1467 = 4808.
Finding tricks that work in base 10 is interesting, but it's a much more fun to look for patterns that work across several number systems. A simple example is for any base > 3, (base - 1) times x where base > x > 1; you get a 2 digit number [x - 1],[base - x]