The dome was designed for robustness: it was stress test to ensure multiple drunk people to could climb on it safely (although this behavior was discouraged at the party).
Most [geodesic domes are designed to](http://www.domerama.com/dome-basics/odd-frequency-geodesic-domes-and-flat-base-at-the-hemisphere/) have a flat base by using a perfect hemisphere. This one was designed to have an additional layer of triangles below the halfway point, giving it a more upright form.