Seeds will not cause seeds in other plants, only pollen causes seeds.
One of your plants has grown male flowers somewhere, otherwise there can be no seeds, but this happened some 3-4 weeks ago, judging by the size and maturity of the seeds in your pictures. One day you will be sitting down smoking when all of a sudden A-HA, a male flower will be looking at you and then you will know where the seeds came from all those weeks ago!
Even feminized seeds are not 100% guaranteed to be 100% female, but 99.8%.
This applies to both auto seeds and photoperiod seeds.
There is no such thing as a stupid question, only stupid people who do not ask questions!
Regards, Organoman.