There's a good YT vid out there demonstrating something similar. A guy does clogs at his computer with a Mic and camera etc. He does an experiment where he explains what the experiment will prove but he doesn't say what the word is out loud at first. He write its on paper and holds it up to the camera. Then he opens several browser tabs to various websites that traditionally have a lot of ads.

He shows you each tab and the ads are not in any particular pattern of interest. He then takes a moment to say the words dog toys out loud and uses them in a couple sentences. He then reopens fresh tabs of the same serious websites and now their ads are for dog toys dog treats dog food.

Google is constantly using whatever microphone you have on a device that's connected to the internet.