(blog author here) Thanks for the feedback. I've raised this issue as well in the past and I think it has already gotten better.
AFAIU there's a dedicated page planned for osh/ysh when you click on the headline which should make it much more clear.
Browsing through the documentation for Oils, it seems to be organized in a way that's very confusing. When you open the fish shell website it was two clear buttons for Tutorial and Documentation.
[0] https://fishshell.com/