Nonetheless, there is some truth in the headline.

When an organ is known to be generated from 2 distinct embryonic preforms, which become merged and integrated at a later stage of development, there is a likelihood that in some distant ancestor the integration into a single organ was much less advanced than now and possibly the two parts remained as relatively separated organs even during adulthood.

There are many groups of animals that include both some species that have retained a more primitive condition, where some nervous ganglia have remained separated, while other species have a derived condition, where those nervous ganglia have fused into a single ganglion.

In this case it is not known for sure what happened, because the early evolution of the nervous system, from a sensory structure embedded in the skin to a complex internal system that mediates the communication between sensors and motor or secretory organs, is still poorly understood.

In any case, this research confirms that the differences between forebrain+midbrain (which includes the cerebrum) and hindbrain (which includes the cerebellum) are very important, because they become established very early during the development of the embryo, at a time when the progenitors of many organs are still interchangeable.