I think they can list anything they want and pay for the privilege.
This has been happening for at least the last six months to a year. Every time I look at an Amazon page, I see totally inappropriate ads, often comingled with a bestselling author's large oeuvre even though I have specifically searched for that author. As an example, when searching incognito for Nora Roberts tonight--who surely sells more books at higher prices than any scammy scummy content mill ghostwritten retreads (have I insulted them enough?)--there is a banner ad at the top from an author basically saying she writes the same kinds of books as NR, priced cheaper, there are two KU sponsored ads next, and only then are there 8 NR novels before 2 MORE sponsored ads for KU books and then 8 more NR and 2 more sponsored ads. All of the KU books are pretty obviously not like NR's. Two ads are women's fiction by Inglath Cooper, who is a well-known author, one an ebook at $6.99--less than NR's prices--and one is a paperback at $15.29, just slightly more than any of the NR ebooks on that page.
Seriously, what is Amazon thinking?
It may be that the cut Amazon gets off the sale of even a high-priced trad-pubbed book is small relative to the money that can be made soaking indies for ad keywords.
I opened a new incognito window and saw that if I searched my own author name, there were no sponsored ads. (I don't know whether to be happy or sad about that.) So, clearly, people are bidding--and bidding high--to be on NR's page. They must be bidding to be on your page, too, or deliberately using keywords for your subgenre. Or both.