I think they had some help, though I can't prove it.
When you add all minimum pledges together you'll reach a sum of 408.810 which is still 100.000 below the final amount.
If every single backer adds an additional 25$ on top of their minimum pledge, then it's still 50.000 below the initial goal.
This is either a desperate attempt from people who saw the campaign fail, and invested all leftovers from their monthly wage (which I think is unrealistic given the high amount of average pledge) OR - what I consider much more likely - some rich people, publishers, marketeers, barons, whatever made gigantic financial injections. If you got these rich people skyrocketing your project on your side, then it's great, but many projects haven't got this luck. GODUS was also a project that would have failed if not "out of a wonder" they "suddenly" reached the funding goal.