I can't tell if you're deliberately ignoring the point: people's public hobby projects may not be _about_ their area of expertise. They may be side projects specifically because they are outside of their main area. It isn't about ability to read code. It's about the difference between what you know well enough to build a career in (and produce non-public work) and what's interesting enough that you'll build it and give it away for fun. They may have very little to do with one another, even if both are expressed in code.
