Power plants are often described in terms of (max) power output, i.e., contribution to the grid. So, I can see how it might confuse a writer to then also talk about storage inadvertently.
But also, the second paragraph already describes the 100 MWh vs MW nuance.
It is not a nuance in an article that focuses on storage from the supposed premier professional association. As an engineer I would expect typical energy content (median/average) of the top 10 hydro pump projects and also some discussion about the availability of suitable sites. I think one should strive for at least high school level physics. There is no need to push out texts that can be easily surpassed by any current llm.
But also, the second paragraph already describes the 100 MWh vs MW nuance.