It's a similar situation because the laws aren't enforceable against the pop-up stores in the same way you can't sue an anonymous subreddit moderator from being discriminatory.
> Likewise, would Reddit force the moderators to allow posts and comments from previously banned users?
In Reddit's case, moderators are using tools that automatically ban users that have activity in specific subreddits. It's not like it's hidden bias, the bans are obviously because of a person's religion.