Do you have some example of something you don't think should be appearing in the results? Keep in mind that there are a few reasons why a word might be thought of as appropriate for a particular JLPT level. There's the difficulty of the word itself, the difficulty of the kanji used to write the word, and then other factors like such as more advanced meanings, nuances, or use in certain grammar points.

In my experience searching with the jlpt-n2 tag on also returns words from jlpt-n5 and so on which is what I think OP is referring to.