If we do give them the benefit of doubt, the other possibilities are:
1. People spam multiple accounts for the app. Reason? Good question.
2. There are really that many people who downloaded the app. Possible? Well, we don't have another union event to disprove this theory currently. Fresh blood that stales quickly might be a thing.
Or we can be the cynist and say nutaku rigged it. I'm siding cynicism actually because of that shitty luck I got from jewelcha... but eh.