It’s cosmetic, but it’s a cosmetic bug: it incorrectly tells the user that they must be the owner of the “relational” when in reality it’s the materialized view.
Materialized views are a type of relation so it is not wrong, just one of many instances where we generalize to "relation" based in implementation details ins team of being explicit about which type of relation is being affected.
So why bother having the error message in the code at all then ? Clearly it was the intent of the author to use this language, unfortunately there was no test to prove that it works.
This is a simple fix why push back ? Additionally it clarifies exactly what the problem is for the user as Jonathan points out.
