This has been bothering me for a long time, I think I may have finally figured out how to turn this off.
To note, I am signed into a private google account on my android phone and tablet. I am not signed intoa google account on my work laptop, yet all google searches were showing up. I turned off sync on the google accounts, this didn't work.
So today I noticed it happening again.
On phone, in chrome browser, select 3 dots in top right hand corner, select SETTINGS.At top beside your photo, click on where is says SYNC IS (on or off).
Select Google Activity Controls, and turn it off (PAUSE) and untick Include Google browsing history and activity from website apps that use google services.
Not sure how to access this on laptop - possible the same if you are signed into a google account, but I am not and don't want to on work laptop.