As already stated, some nanners probably formed halfway through flower, and pollinated some of the buds a few weeks ago. Those look too young to be any good, but they will be all female if they were self pollinated.

Some strains do this genetically in perfect conditions, others do it because of stress. If the seeds do germinate, it's highly likely that they will throw out nanners also (for the same reason as the parent plants - either genetic or stress related).