Thanks everyone. I feel a bit better knowing that I wasn't the one who killed him, even though I'm still sad he died like that. At least he had a few hours in a nice tank.:)
Since I made that post earlier I finished cleaning and resetting the tank (the gravel and conditioner I purchased new with the original fish, since twilight storm mentioned them).
I have another betta in a very large punch bowl waiting for the tank water to heat up and for the conditioner to run through with the filter so I can float him and introduce him in a few hours. I was going to wait a few days before getting another fish, but when I was at the aquarium supply shop I took a look at their bettas and was very drawn to him.