Neither Reddit nor lemmy meet the actual requirements of social media.
- Knowing the people you are talking to. Both Reddit and lemmy are anonymous
- Status updates on some sort of timeline.
Lemmy and Reddit are forums of forums, and if you want to get more specific they’re link aggregators. Nobody ever called the car forum you visited to ask for car help “social media” because it wasn’t and still isn’t. Same applies to lemmy and Reddit.