Sure, they retarget ads they think you might want to see, but the difference is when using Google you are actively looking for something, not passively.
Google looks at both your current search/browse activity and gathered data (the gathered data being especially important for all the very many Google-served Ads off of google.com)
Facebook also looks at your current search/browse activity and gathered data.
The only real difference is Facebook search is universally entirely worthless so far less of that signal gets used relative to more passive snooping.