The code in the article is not wrong. It is not unsafe. The author explicitly handles the OOM case correctly. It is true that there are more optimal ways to do it if you do have an OOM handling strategy.

And no, you're not supposed to teach your students the best way to do things at the start. That's not how teaching works. You start with the simpler (but still correct) way, and then work towards the best way. This is why introductions to Rust are full of clone calls. The best Rust code minimizes the number of clones. But when you're introducing people to something, you don't necessarily do the optimal thing first because that disrupts the learning process.