If the temp didn't drop far below 70, I doubt it was the temp. Glowlights, as well as bettas, are tropical fish.
Sometimes filters can be an issue with small school fish such as glowlights, neons, and cardinals. Were they stuck in the filter? If not it probably wasn't the filter.
I could have just simply been stress moving to an entirely different inviroment. Alot of fish get stressed when making transitions. I use a bacterial suppliment that is supposed to help reduce that, and from all my expirience, it has worked wonders.
Did you use any new chemicals? Do you have any decor that wasn't pruchased for aquatic fish?
It could have been the water chemistry. Glowfish prefer soft to slightly basic water. If you have a very alkiline water, and your lfs kept them in water in their prefered range, the shock of sudden chemistry change might have done something like that.
If the tank that they were in wasn't cycled, the sudden rise in ammonia may have injured them, but I doubt that the ammonia would have raised that high overnight.
Not that this has anything to do with what happend to the fish, but glowlights and other small school fish should be kept in groups of 6, minimally. That way they will all feel safer and live longer, happier lives.
Very sorry for your loss.