The brewery describes the Belly Button Beer as a "new world-ish Belgian-ish Witbier with fresh orange zest and toasted coriander seeds." As explained in the report, it's a "spontaneously fermented beer," which means it's also exposed to naturally occurring yeast and bacteria during the fermentation process. Additionally, the brewers added Riwaka and Mosaic hops to boost the citrus flavor profile. Oh, and probably cover up all that hot bellybutton flavor.
As for the actual belly button yeast, there's a whole other level of scientific process behind that, which we'll allow the brewery to explain via a blog post on its website:
"The process of isolating our own yeast strain involved swabbing samples of each of the brewer’s belly buttons and getting our full science on by streaking out the samples on agar plates. After allowing the plates to incubate, we found all sorts of interesting things growing, including what appeared to be colonies of yeast. Positive controls were used to help us identify yeast colonies and negative controls were used to ensure our techniques were sterile. We selected individual yeast colonies and grew them up until we had pitchable quantities for trial batches."