Was just reading more on the Montgomery curve under the arithmetic section, I think we are safe to "ignore" z, him saying z=1 allows us to say X=x and that's all we need the z for.
A point P=(x,y) on the elliptic curve in the Montgomery form By^2 = x^3 + Ax^2 + x can be represented in Montgomery coordinates P=(X:Z), where P=(X:Z) are projective coordinates and x=X/Z for Z!=0