I've grown red bell peppers for a few years and was excited to pick my first one this year only to bite into it and find it was hot and spicy! It is growing near a jalapeno just like previous years.
Why Is My Red Bell Pepper Spicy?
Looks -- or rather tastes -- like there was a hot pepper in the wood pile! Hot peppers and sweet peppers are very closely related, and while growers do their best to produce plants and seeds that have the particular set of characteristics that have been advertised, plants sometimes have their own agendas. Hopefully, if you have more than one plant, they won't all be hot.