I remember R. Feynman wrote that at some point in his life he reached the end of his achievements, and it was a pretty sad time. For many years he couldn't produce anything valuable anymore. So over time he gave up trying and just kept on living, doing stuff just for fun, not for value. One day he saw someone juggles a kitchen plate throwing it into the air, spinning. He got interested, why does the plate "waves" exactly twice less than rotation speed. He started computing it, just for fun. Because he was already a failure, so who cares. Over time that pointless kitchen plate computations grew up to quantum calculations, for which he much later was awarded a Nobel.
It is a miserable life to treat everything like a chore done to earn some know, expected, concrete reward.
I suspect the author got curious, did some reading, realized they understood something, and thought it would be fun to write up the result. Likely all in their free time.