Yes - by most definitions. It's powered by user-generated content and is based on interaction between users through engagement with that content, which is voted and scored.

There is a difference which I personally feel makes reddit less harmful than other social media, however, which is the algorithm - or lack of it.

In most social media, the algorithm exists to continually serve people the exact content they engage with in a constant feed, which is IMO the most socially damaging part of social media because it creates endless doomscrolling, toxic echo chambers, promotion of sponsored content, and a whole raft of psychological problems in users.

The Lemmy homefeed is more organic, and scrolling through 'all' you see content genuinely from everywhere, in a less curated way based on upvotes, not individual algorithmic tailoring. And that's maybe not as "engaging" but it's far less damaging.