I'm part of an Adventurer's League group at my local store. About 15 people play, split among three tables/three DMs. Originally we'd all been running Harried in Hilsfar, but I'm under the impression other tables are doing a different adventure as we begin Rage of Demons.

Tonight was the first RoD session and one player, who has always meta-gamed pretty hard, meta-gamed really hard, having already played the content with another group. I would ask the DM a question in-character, he (meta-gaming player) would out-of-character explain things none of us could possibly know at that point, etc.

The DM got understandably frustrated and scolded him pretty harshly. "Player, we talked about this. If you can't stop doing this you're going to the other group next week." A bit harsher and wordier than that, but that was the message. It was awkward for the table, but we moved on. MG Player was quiet for a while, but eventually seemed to shake it off and try to play again.

Unfortunately, he continued to MG. I don't know the player well, but my impression I've gotten from the time I've played with him is that he loves learning the content, and if he has knowledge to share he is excited to share it. It is a problem that needs to be fixed, but I also think is a personality trait of the player that he may need some help working on and can't flip a switch and fix.

However, when he started MGing again the DM got understandably very frustrated and said essentially, "No, I told you, I'm not having this in my game, you're playing in another group from now on." The player did sincerely apologize and seem very sullen, but the DM wouldn't hear it and "banished" him to one of the other tables next week. (This means he will likely be playing with the rowdy 10-14 year olds from now on, something our group got together to avoid.)

I think the DM was entirely right that this sort of metagaming cannot happen, but I also felt really uncomfortable when he had this exchange at teh table. I don't know what he could have done differently, and honestly even if I did I don't feel it's my place to say "Hey now, stop." and just add to the table drama. All the same, they were awkward exchanges to sit through for all the people at the table and I left unable to speak to the player, but feeling incredibly bad and empathetic. He was just excited. Did he need to be scolded? Yes. But publicly kicked out of the game? :S

Anyways, the moment is gone regardless, but I'm wondering if other people have witnessed or been involved in such events, and what you might recommend to anyone (a witness player, the metagaming player, or the DM) so I can keep it in mind for table etiquette concerns/future DMing advice?

TL;DR: Metagaming player publicly admonished and removed from our Adventurer's League group by the DM mid-session. It was awkward to watch and I have tremendous empathy for the player. I didn't get to speak to him after the event, however, and I'm not sure what I would say if I could. Any advice for these sorts of scenarios from here on or if something similar happens in general?