Yeah that could be worded better. No units. Resumably it's about the number of visits.
Looks like that number lines up with their reported DAU (daily active users) metric rather than site visits.
52 million DAU is about where Reddit was in the summer of 2021, per data on Statista. It also tends to vary up or down by a few million at each sample point, so we'd really have to see a long-term trend-line rather than a 2-week data snapshot to know whether the blackout had any real effect.