When you do any search putting the word in the search terms box, the default sort order gives you the recipes with the word in the name first, which implies it is a main ingredient rather than an incidental. So when I search the Library and get 4,943 results then all the top recipes will have radish in the recipe name.
If you are specifying radishes in the Only Show filters, which is the correct thing to do to get a very exact search, then refine the search by also entering Radish in the word search which then sorts by relevance i.e. makes the recipes with the ingredient named as the top results.