All peppers are the same species, actually, from your basic sweet bells to the hottest reapers and ghosts.
It’s all breeding. It’s like what we’ve done to dogs: they’re all the same species too, but their physical characteristics vary wildly based on selective breeding.
Some varieties do have wildly varying spiciness. Shishito peppers, for example, are mostly entirely mild except for about 10% of them that are much hotter. Never know what you’re gonna get. At a restaurant level, you just accept that some batches are going to be hotter than others. But, overall, growers can select and control what they grow well enough to make most of them mostly consistent most of the time.
Chilli’s cross pollinate really easily, resulting in that variation of spicyness. Controlled pollination (specifically from controlled stock) growing conditions, and regular testing of capsicin levels allow them to create a more uniform product.
This cross pollination ability is also why the hottest chilli in the world is constantly being updated.
When I eat Jalapenos from the three plants I had this year, I take out the seeds and the soft tissue they are attached to. Most of the heat is in the seeds and that tissue. Without it I can just munch on them raw.
So maybe the variation in heat you are experiencing is due to the varying amounts of seed and connecting soft tissue in the peppers.
If you have a garden, you have like one plant, and the bee pollinating the pepper may have pollen from a different pepper species, so that makes it far hotter or milder.
When you grow commercially, you have several acres of the same pepper, same species, same seeds, same hotness; almost everything coming outta the same farm will be roughly the same.
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