Why after I gave him a new outdoor home he died?

My rabbit that I've had for 6 or more years was inside in a cage 24/7. After several weeks of contemplating and getting advise I gave him a new outdoor home. I thought it was for the best and he would be with other bunnies and have all sorts of room. This was last Sunday. I got a call on Wednesday from his new owner telling me that he had past away. I just dont understand. He was eating, drinking, and socializing. I cannot help to blame myself. I just dont know what to do. He was very well taken care of and cuddled with. I loved him dearly and thought that I was doing the best thing for him. Any advice?