Google tailors its results to what it knows about you, which is not just your search history, but is also anything that google has managed to learn about you. I don’t think google has ever published exactly what data it keeps about you, but we know that they examine tracking cookies and track what you do on other sites, and especially on google-owned sites like youtube.
You can disable google’s personalized search results. Go under your search settings and look for the section labeled “private results”, and select “Do not use private results”.
If you go under your google account and select Manage Your Google Activity, then select Go To Activity Controls, you can enable or disable what data google tracks on your account, including:
Web & App Activity (what you do on any web site or app)
Location History (your physical location, based on IP or GPS)
Device Information (contacts, calendar events, what apps you have installed on your device, etc)
Voice & Audio Activity
YouTube Search History
YouTube Watch History