I assume since they're a viral / addictive platform the numbers will be higher. Plus they're not a blog or so, but rather a personalized social media platform, which makes stuff more complicated (you can't just cache their news feeds, they're all personalized).
It's easy to say meh, 11m is nothing, there are other platforms with more users (esp. since you don't bring up examples how you managed otherwise). But I think it's a big technical feat to do this with 6 people.