So sorry to hear about your new frog. :-(

I would doubt that the misting did your poor little guy in. I would guess stress more then anything was a major factor.

The pet store should replace him and I would just ensure the new frogs basic needs are met such as temp, humidity, declorinated water dish, and things to climb, perch, and hide on.

Misting water can be Distilled, Bottled Spring, RO or Declorinated Tap water. Water for the dish should be Declorinated Tap or Bottled Spring was as long as the spring water states it has no chlorides.