That's seeds alright. To be that mature that plant must have had contact with pollen weeks ago. Looks like a 4 week seed. They take 5-6 weeks to mature from the day they got pollinated. It's not hurting anything so might as well leave it until it ripens.
Have you had a male plant in your grow room prior to these plants flowering? Visit a friend with male plants then go home and play with yours? Pollen had to come from somewhere.
I don't see any sign of 'nanners but I can't see much of the plant in the pics. They can be hard to find and look like this. May be white if older and dried up.