It's important to understand what the functionality of a Filter is.
The reason why a user would apply a filter is to weed out results that
they don't want.
If no filter is applied, the user expects to see all the results.
As far as the "showing all results seems non-intuitive" is concerned; that is a whole different use case on its own. That depends on how the results get shown. Is it a list that gets populated as soon as you open a certain page? Or does it get populated by a user when they use a Search functionality? But I don't want to get into it because it's not in the scope of this question.