True, but there are plenty of programming side projects that don't require an Arduino, and we often get in our little tech-bubbles and think that the internet is more of a monoculture than it actually is. I've heard (a lot) about the Arduino, so I may not be the best example, but my programming side projects are more likely to use Processing, Cinder, VPT, or some other thing that doesn't necessarily need to interface with that kind of hardware.

If we're talking about the original article, side projects were mentioned in the context of "The instinct to experiment first". There might be some correlation there, but if you limit the focus to programming side projects you've just chosen a slightly bigger box to experiment in.

Many advances in science come by drawing knowledge from a completely different field and applying it to a familiar one. Deep knowledge of programming is necessary but not sufficient for creative programming solutions. Design patterns in software, to take one familiar example, are based on Christopher Alexander's theories about physical architecture. The article itself recommends amusement park rides to foster greater risk-taking. Non-programming hobbies can have great benefits for programmers.