Google has mixed its search ads between and throughout the organic (free) search results starting sometime mid-last year. Google calls it dynamic ad placement, and it is an ongoing tests. In fact, Google had to change its definition of top ads to make way for this historically very unGoogle-like move.
Anybody still using Google should take a deep long look in the mirror. Not for any moral reasons, just a sort of “how much do I enjoy wasting time skipping adds” reason. It’s what made me switch to a different search engine. Because Google is becoming borderline unusable with how far down the actual results are now.