Although some images related to your search show up from sponsored web pages (notably shutterstock), they can hardly be labeled as adds. The section is well identified, related to the search, and does not make the page feel too distracting or unclean.
All imagery on pixbay are under the absolutely permissive CC0 licence. (Although material that appears within the images can be subject to copyrights) https://pixabay.com/en/service/terms/ "Images and Videos on Pixabay are released under Creative Commons CC0."
Since pixbay is a free user driven service, it can be difficult to find some pictures related to the subject one is searching on. While in other instances, a flood of results appear because it is a very easy subject to shoot. eg. Road (flood of options), Surprise (Debatable options)