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.
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.