What is this mysterious dot in the Message app?

I've noticed for the past month that there's a dot that appears next to my friend's name in the Messages app. It only appears next to his. When I get a new message from him, it's not fully blue. And when I open the message, the dot remains, but it turns gray. I'm thinking it has something to do with Do Not Disturb mode because when he sends me a message, I get no notification alert or sound. Has anyone had this problem? I've attached screenshots as well.