I didn't exaggerate anything. Two years ago they were growing at 200-300k users per day. Dave & Ami were using those numbers in public talks. So, let's be generous and say instead that 700k users represents two or three days worth of growth rather than one.

It actually doesn't matter with respect to the more salient point, which is that talk of "statistical significance" is irrelevant because the calculations require an unbiased sample. As I outlined above, there are at least three strong reasons to suspect this poll is irreparably biased.

Self-selection alone is typically enough to condemn a poll. Look up the history of Gallup if you want to see the real-world impact of self-selection in polling.