Although I agree that this is a great customer to land with a...

Although I agree that this is a great customer to land with a massive user count, I think it would be safe to assume special pricing was applied. They are using them as a reference and have been part of the marketing push with the SharePoint Home Site announcement.

I'm sure the deal was still massive and the landing a customer of this size will open other doors not previously achievable, so it's a win for everyone involved.