Unfortunately your calculations are based on partial information.
If you want to estimate the willingness to pay $50 or more, you should take under consideration the fact that of those 15,623 Kickstarter backers only 3,693 of them decided to pay 50$ or more. Your assumption that there are actually 15,000 super fans who will pay $50 or more is not supported by any information that we have.
Your conclusion “Games cost $1m. KS raised $600k so it must have made $400k or more.” is unfortunately not correct. A more correct one would have been “KS raised about $600k. Additional investors paid $500k. So they collected about $1.1m and that tells nothing about people’s willingness to pay.”.
There are several threads and posts in which Ron provided additional information that is required to get a correct picture of the situation. Maybe the following post is a good start to acquire that information (notice that it was written before they broke even):