The site says
"This circuit uses avalanche noise in a reverse-biased PN junction, the emitter-base junction of the first transistor. The second transistor amplifies it. The first two ALS04 inverters are biased into a linear region where they act like op amps, and they amplify it further. The third inverter amplifies it some more..."
Which basically boils down to a reversed PN junction creating random noise, which is amplified. That sounds simple
Luckily, our ears don't care how random the noise is.
True, a project like yours doesn't need true randomness, but then there's no harm in having some anyway...
Serial because I can't really use push buttons because I don't have a breadboard. I do have several pushbuttuns due to me disassembling random electronics
If you have a soldering iron and some loose wires, you could solder the terminals together and get away without a breadboard. If you don't have a soldering iron and some wires, you're missing out on fun!