Indeed, it is a qualifier. A qualifier that the botanists widened. When they said “you can make a fruit salad with tomatoes” they used their definition of fruits, but the narrower definition of cooks for “fruit salad” (there’s no botanical definition of “fruit salad”, it’s a purely culinary term). Thus, we have a category error.
Yes we have a category error because you made it The botanist is narrowing down the category of salads by qualifying it to be fruit salads.
On the narrowing side that category error is generally not present, say, you can narrow down “fruit” to “tropical fruit” or “temperate fruit” and still get perfectly valid fruit salads made from those narrower categories. Heck you can narrow it down to “banana” and get a fruit salad, even if it may be a bit bland.
Yes you’re right in this example the qualifier is tropical that narrows down fruits. In the previous example we talked about fruit salads. The category being salads.