It depends on the things that you want to learn and amount of extra work you want to put into it. For instance, I used Go for the most of AoC 2018 problems and I had always been using C/C++ in algorithmic contests when execution time mattered. And yet, I wouldn't say I know any of these languages good enough to write a production-grade system because I only learned usage patterns common for small, write - run once - throw away applications.

On the other hand, the author of that post seems to have used a lot of more complex language features, did profiling, debugging, made use of many libraries etc - a lot of extra stuff that wasn't necessary to give correct answers but is crucial in 'real world' programming.