Google automatically saves contact information like names, and email addresses from different Google products. These are Google interactions. So, when someone shares a document with you or is in the same group or events, their information will be auto-saved in Google. This can be turned off if needed.
Here is how:
Open your Google account page and click on People & sharing.
Scroll down to Contact info saved from interactions and click on it. By default, it will be enabled.
Turn off the slider next to Save contact info when you interact with people.
This will prevent saving contact information from different Google products except for Gmail.
Also, for managing existing contacts, you can use the Google Contacts tool to add, edit and delete them.