It breaks down to the process of cellular respiration as the microbes breakdown the "food" in the bucket. Aerobic cellular respiration is obviously when the bacterium utilize oxygen within this process to break down organic molecules. Certain byproducts result due to this breakdown and these are (respectively): ATP, hydrogen, carbon, and oxygen (of course there are other byproducts, but these are the main items seen as an end result). ATP is formed, hydrogen and oxygen pair (water), and carbon and oxygen pair (CO2)-----> Carbonation and a foamy head result. So long story short, I believe you are correct in regards to aeration aiding in head production to an extent, but also the natural production of co2 aids with head production as well.
This could mean that a good head in your tea indicates adequate aeration and aerobic microbe reproductivity.
....damn, my head hurts...haha