The code has a pretty detailed breakdown of what each part is but the general breakdown is that most people make transactions around dollar based amounts. If you look at all the UTXO for the day you'll be able to graph that into a bell curve and find the average pricing people are splitting their UTXOs into (based on their sending amounts usually being tied to dollar amounts verses Bitcoin itself being the unit of account.)

I've not done an analysis of the data but I think I read its fairly close to what market prices were for the days it tracks. It only goes back to July of 2020 presumably because there was less USD based transactions before that period and thus denominations would be tougher to pick up on in the on-chain data.

This is just a common heuristic. If say BRICS were to adopt bitcoin around a pegged gold currency and there were enough people not using USD as their unit of account this heuristic will certainly break. Until then it's a pretty interesting set of data analysis.