If normal type moves can't hit ghost types, then why did my gastly sustain damage?

Question

I was battling whitney, and her miltank used stomp on my gastly, and it lost half of it's health...

Answer 1

Its because Whitney's miltank's ability is scrappy which allows normal and fighting type moves to hit ghosts.
Source: http://bulbapedia.bulbagarden.net/wiki/Whitney

Answer 2

Maybe the miltank has Scrappy.