If you are referring to the jade, it is not in the cactus family. They are both succulents but that's about as close as you could lump them together. Thus, I don't know whether your plant was a jade or a cactus. I can pretty much assure you though, that it rotted because of water. I would have to know what sort of potting mix was used, what sort of drainage was present, what size pot it was in, how much cold was it subjected to, etc. to help you. As you can see, there are a lot of variants that can lead to "over-watering" problems.
