Bad. A 70W HPS is 55V by 1.6A. A 70W MH is about 80V by 1.0A. So the lamp was underdriven, running at about 40W, and the ballast would probably eventually overheat.
You haven't quite seem to have gotten yet that two different types of lamps of the same wattage usually aren't compatible.
![Tongue :P](/Smileys/default/tongue.gif)