Maybe they forgot to add "in their opinion"? Or maybe the dialog should have been around what is a refugium to you (guest, 2nd party in the content) and how is it installed, implemented. It really comes down to the hobbyist, use case, and how they implement it.
- Is it part of the sump
- Is it separate
- Is it used as a "refuge", safe place for organisms free of predation
- Is it setup such that there is a path from refuge to display for pods to feed display mandarin (example)
- Is it used for filtration or export of nutrients
- Is it used to grow macro algae for primary display food
- Is it used for observation of new fish, corals
- Is it used for time out
- Is it used for treatment if it can be isolated
- Is it started with any or several of the above but later ignored for various reasons and now a junk drawer of sorts