If you read this Is seeding peppers a must when making hot sauce it is made pretty clear that chili seeds contain little or no capsaicin but are bitter.
I have personally experienced (and then made) a very hot condiment made by cracking chili seeds with a spoon and mixing them into soy sauce then leaving it to stand. It was pretty potent but the seeds could well have traces of the placenta attached to them.
Is the spiciness entirely attributable to capsaicin from placental contamination? Or is there some other mechanism at play?