It's not clear to me if the author actually understands how staging works and how that affects the commands they suggest. They claim that stashing takes staged changes and then note that after stashing the working tree will be clean. That suggests the post is being dumbed down or the author is misunderstanding things.
Git guidance should almost always start with a brief introduction to the concepts you believe the audience doesn't know or fully understand. To begin with reset and not properly explain the index will just end up being confusing, especially with brief references to hard, soft and mixed resets later on!
I see this so often with power user tools. All power user tools are tools that you can only use reasonably well with some basic understanding. They are made not to be understood in the easiest fashion but to handle all complexities of a problemset as efficiently as possible. Therefore it sometimes seems harder to use from the outside, but actually the hardness comes from the problem it solves, not the tool.
So yeah, if you really want to use git well, learn its internals. It takes some time but actually not even hard. After reading the Git Book once I was even able to implement my own git (of course without performance considerations).
Git guidance should almost always start with a brief introduction to the concepts you believe the audience doesn't know or fully understand. To begin with reset and not properly explain the index will just end up being confusing, especially with brief references to hard, soft and mixed resets later on!