science

Yea, most musicians are generally not that well off and have as much free time as you think. Most still work some sort of regular job to offset the cost of living and equipment because they won't make the money they need to survive solely off of the money from gigs. They do it because they love it and not because they're making tons of money and have ample free time. Their hobby is music, so whatever downtime they have from regular life, they fill it with playing and writing music. If you're fortunate enough to be signed to a label, you're on the road for months out of the year gigging and constantly immersed in your music, and that definitely isn't a health benefit either. There is a thing down here called the Musicians Clinic - musicians don't have a typical job and therefore don't have access to medical insurance like they would if they worked a 9-5 with benefits, so it supplements that to keep them healthy.

Source: from New orleans, have family that plays music for a living, play live music myself, and know tons of gigging musicians.

The study referenced cites another study that showed the causation in kids for music and cognitive skills. So it's a good question to ask

Hank's Razor: if something can be explained by socio-economic status, it's probably that rather than the thing that you're measuring.