There's of course nothing wrong with re-implementing 'ls' in C with all the same patterns, and sure, that could be fun, and maybe even earn a slither of respect, but no-one is going to care about your project as something useful or interesting, quite rightly.
The article isn't just saying it's "absolutely fine" to make software for fun/practice, it's complaining about other people having utility-focused questions and evaluations. Assuming that "show it to your friend" is supposed to be an analogy for more general showing off, reactions like that are plenty reasonable. If it's software nobody is intended to use then that should be made clear up front.
As a software example, 'ls' but written in rust.
There's of course nothing wrong with re-implementing 'ls' in C with all the same patterns, and sure, that could be fun, and maybe even earn a slither of respect, but no-one is going to care about your project as something useful or interesting, quite rightly.