[stfwn]

I have been in music for some time, and this is almost exactly what great musicians do. There is definitely a time for activities that are ‘neccessary’ or ‘good practice’ to spend time on, and then there is a large amount of time they almost subconsciously spend in their field: they just enjoy having a beer with friends (at a jam session), having a chat (about music), hanging back (with their instrument), waste time on YouTube (watching poor quality phone recordings of musicians they look up to). Some don't think about anything else. Some have other interests. But I cannot think of one great musician that doesn't touch music when they're ‘off from work’.

[Retric]

There is a difference between coding in your off time and reading Hacker News. What you're describing is someone who is relaxing not working. Aka great don't work long days mastering an instrument, just put in their 9-5 and casually have fun. So sure, if someone does not keep abreast of computing in their free time that's not a great sign, but deliberate practice works best a few hours a day not 10+.

PS: What side projects do provide is a way to have more experience than your number of years in the field would suggest. But, that has heavy diminishing returns.