Seeds don't spread seeds, only pollen can make a seed in the bud. The green thing you found in the bud is a seed pod. Over trimming during flower could possibly do it. More common is a light leak or disrupting the plants night cycle.

Some strains will turn on you very easy others strains take more abuse. But it is always a good idea to check your plants. BTW did you find anything near the node on any of the plants that could have been a pod at one time? It is very possible the plant with the seed is not the one with the naner, it could be any of them.