The researchers suggest that these relocating neurons are only temporary guests in the larval mushroom body, taking on necessary larval functions for a while but then returning to their ancestral tasks in the adult brain. That’s in keeping with the idea that the adult brain is the older, ancestral form within the lineage and the simpler larval brain is a derived form that came much later.
I mean, from my understanding of Japanese, this makes sense. There's certain humor and puns that exist due to the usage of Kanji and its meaning (that typically get lost in translation).