As someone who has rooted hardwood (and semi-hardwood and softwood) cuttings for 35 years, this simple approach does work for a select
number of species. It is very easy, and something everyone could (and should) try.
But, don't be dissuaded if results are disappointing. The writer's mild winter climate (which he does not mention) is a critical factor with this regime, and most hardwood cuttings will require a rooting hormone (usually IBA) or a greenhouse intermittent misting setup (or some such additional accommodations) and for some, a 12-18 month period.
As I mentioned, the simple method describe in this garden idea will work on a small subset of woody plants. It's a great first introduction to stem cutting propagation.
However, I might suggest that the writer list the species with which success was achieved, so as not to set up a novice to fail.