It's not about fungi making cheese. We know that bacteria are the largest component of the microbial community making cheese. The point is that aliens traveling through the enormous, barren-of-everything wastes would likely know how to use biotechnology, such as fungi and bacteria, to replicate the life cycles found on their homeworld. In ours, it's fungi breaking down organic matter, bacteria turning nitrogen into nitrates/nitrites, cyanobacteria turning carbon dioxide into reduced organic (carbon) compounds, etc., etc. In theirs, it could be strange silicon/phosporus/sulfur forms (unlikely, due to a bunch of esoteric but important rules about the chemistry of those elements) being processed by microbial life. After all, do you think a single celled microbe, or a relatively giant multi-cellular organism will arise first? If life there is anything like here, the single-celled organisms will be the foundation of any multi-cellular organism's environment, each contribution of the microbes shaping the biochemical pathways that the larger organisms will use merely by providing building blocks and affecting the environment, ala the sudden explosion of atmospheric, gaseous oxygen when microbes began to explore the pathways of photosynthesis.