Seeds formed only on single calyxes at nodes

Do you know what would cause seeds to form only in this spot? I was trimming up some plants and each plant had maybe 5-10 seeds only in these areas none inside the actual flowers. No signs of any male flowers anywhere. All the seeds were fully mature so they would have had to been pollinated around midway through flower.

An early pollination of the pre-flowers... maybe the pollen wasn't viable or present when the actual flowers were fertile.

On the other hand, this pre-flower seeds tend to be very healthy and specially big.

CHeers.