The given linear function is f(x) = x-2
The parent function of this linear equation is y=x
Your friend's way of explaining this function is not quite correct.
If the transformation in the function is of the form [tex]y=f(x)+c[/tex], then the graphs moves up or down vertically in the y- axis direction depending upon the value of c.
If c>0, then the graph moves up.
If c<0, the graph moves down.
Comparing the given equation [tex]y=x-2[/tex] with [tex]y=f(x)+c[/tex], we notice, c = -2 which is less than 0.
Hence the graph moves down by 2 units.