I recently noticed that in my phone contact list (which is synchronized to the Gmail contacts) there are many contacts that I don't remember adding and that I don't even know.
Has anyone else experienced this? Do you know what could be causing it?
This is often caused by linking other social networks (via the appropriate App) or third party E-Mail providers to the Android device. This will cause the contact lists or address books to be synced and shown in your device.
This includes for example
Besides the source mentioned by Flow, since Gmail may, depending on your settings, automatically add people you send messages to to your Other Contacts list, that might also be a source of unexplainable contacts in your contact list.