I heard that if you plant normal peppers next to hot peppers, the normal will have heat also. Not sure if it's true tho.
Have you grown them close to each other?
As others had mention already it cannot be true. I've heard of this misconception, we even had a thread about it here, but it's not proven yet. Although there are some thoughts on the peppers placenta getting the heat or even the roots interconnecting. Anyway that is not the case for sure as I had literally hundreds of plants all getting more heat, regardless of the place in the garden or pot, and I had very few sweet varieties.