Ello's got at least that many daily actives, and about 200k monthlies. That's much larger than Facebook's founding class, though also a different mix.
It's also worth realizing that many influential online communities were very small relative to their impact. The WELL and Usenet had core userbases in the tens of thousands of users, best I can make out.
I'd chalk Ello's exposure up to a few factors. One was the whole "David vs. Goliath" meme that struck when Ello was first revealed. World+dog are trying to figure out how to take on Facebook, and that's how the story was pitched. Ello's leadership makes quite clear that's not their take on things. Another was that, at least for a time, Ello had attracted quite the credible crowd. Clay Shirky, Charlie Stross, Bruce Sterling Paul Mason (UK/BBC journalist), Quinn Norton, Meredith Patterson, Tim Bray, danah boyd, Jonathan Zittrain, and others all created accounts, some posted for a while, a few still do.
It was too early. I've posted a few long lists of features Ello desperately needed to be viable, and lack of those, along with various bugs, were really hampering it.
While it's still got some technical shortcomings, the team's been addressing them quickly, doing a good job of it, and surprising me with some quite ingenious (and not always technical) solutions to problems or ways of offering capabilities. And they've directly addressed most of my major issues. That responsiveness has been notably missing at Google.
The site also has quite the creative set present, which tends to be a good early adopter set -- think artist colony.
But technical features and a cool vibe aren't enough. Though they're a good start. I'm encouraged by the feature set, community, leadership, direction, and foundations. Rather more so than by a few other systems -- G+ was already faltering badly in its first months out of the gate, Ello's avoided those faux pax entirely.
I'm also getting some sense of the HN effect: a front-page placement seems to be good for about 3.5k hits in 3 hours or so, based on this item.