C syntax is limited and therefore "simple". Building advanced data structures and programs with your limited toolset does require some out-of-the-box thinking.

This is partially why C is a common teaching language. Because you have to build a lot of tools that are easy to take for granted in other languages. Take a Map or Dictionary for example. C doesn't technically speaking provide one, so you learn to implement them pretty quickly and often. Technically speaking C doesn't even have a primative string type, you just create an array of chars, which by the way has to be a pointer. While this is super easy to do once you've seen it once or twice, it teaches you how strings work in almost every other language.

The reason you can trivially loop through a string in python, is because it works the same way, they have just abstracted it a tiny bit from you.

Now to the author's point... does that really make you a better developer to know that? Therefore is it really needed? No probably not needed. But these exercises and experience does help solidify more complex topics later on. So you don't need C, but I still think there's benefit in learning it.