Yeah, it must be specific subreddits they've posted to. Other than spam flagging, I've never seen reddit itself restrict links. It's pretty common for subreddits to use AutoModerator to enforce a link allowlist, however.

Reddit should probably take some steps to help users understand the difference between Mods and Admins. It's extremely common on reddit for users not to know the difference. They are always taking the heat for something some random user did to a subreddit they moderate.