I believe the statement you cite is not meant to mean GtS *per se*, but the Fediverse as a whole. In that paragraph, they're opposing themselves to stuff like Twitter (where Elon *is* the "must-follow" influencer, whether you like it or not), Facebook, etc. But also, unlike Mastodon, it does not have a "Trending" view of posts and hashtags, so their only algorithm is ORDER BY date DESC.
So, I don't believe it means the load. If Ruby-based Mastodon can sustain huge servers, Go-based GtS should probably be even better at that.
