These are two completely different conditions - the requirement of a change in dipole is not the same as the requirement for a change in the quantum number of ± 1. Both requirements can be derived by evaluating the transition moment integral, but that's a fairly advanced mathematical exercise. The dipole change condition is easily shown by symmetry considerations.
You can see a little more here
, although this link doesn't provide the actual derivation.
Note that the Δν = ±1 selection rule is only strictly valid in the harmonic approximation. In real systems that have anharmonic contributions, overtones with Δν = ±2, etc., become weakly allowed.