A number of people recently have asked about the difference between commenting in a Doc and the words you see when you open a Google Doc - Type @ to insert.
In short, when you use the @ and then type in someone's name the following becomes available:
When you select share, it will then bring up the sharing settings.
Also, when you select their name in the Doc you will see the ability to quickly send an email, message, video call, and schedule an event. If you select to see the detailed view you will see the latest interactions as well as the other mentioned options.
When you select the comment feature you will see what you see below. If you would like, use the @ to include a person and send them an email (and assign the comment to them - see second image below).
Embedded below is a 1 minute and 52 second YouTube tutorial.