You can see how that number is derived in the post. It's based on very optimistic projections from data that reddit has previously released about their revenue, and very pessimistic projections of their user growth. If reddit somehow has massively increased the value they can get from each user compared to that I think the burden of proof is on them for that.

From TFA, $0.12 is an optimistic calculation taking better-than-best revenue divided by a pessimistic user count. We can double that again if you're expecting a late-stage product like reddit to launch a new highly monetizable feature soon, and it's still quite far away.