I think this is roughly equivalent to their point: Pi is a rational number, as long as you're in base-pi

So a bubble is unary in that it represents pi with single molecules in a circle. Then, forces tug at it--like gravity a tiny bit, but moreso wind and especially the hyperlocal flow of air driven by eg temperature (and particle concentration) that want it to not be spherical. But the bubble membrane wants to be spherical because that's its most stable shape. Here we're thinking of big huge bubbles, those exemplify this more, bubbles like 20 cm in diameter. So it's a tug of war between the air and the bubble, with the air tending to infinitely deformed and therefore inescapably burst bubble and the bubble tending to pi.

It's an analog approximation of a sphere against the error induced by air motion, and gravity.