I have created a list and have added a Column of the type "Person or Group". I have limited this field to just look into a SharePoint group to get an option
When I go and add an item the People Picker shows users who are not in the SharePoint group defined. If I select them validation kicks in which is good.
Your organization's policies don't allow you to share with these users. Go to External Sharing in the Office 365 admin center to enable it.
Is there a way I can stop these other users from appearing in the People Picker?