Someone likely complained to the mods, like that guy in the comments. The session videos were never removed, but I'll make a note of not linking the orgs in the comments, so as to not give them excuses to complain.
I've seen videos that have have advertised orgs before on the subreddit, but I think they get away with it because they're more well known and/or less blatent with the advertising. The latter is why I think the session gameplay videos didn't get flagged.
At the end of the day, the video got views, so the reddit post did its job.