It does appear to synthesize the audio with a wasm module compiled from rust, presumably developed as a python script first based on the source comments.
To the credit of the author there is also an attribution file which describes a process of deriving the models from recordings (none of the techniques are very novel, but it's fairly impressive to see automated -- edit: I assume the project is LLM-generated) https://github.com/celphase/duck-pond/blob/main/ATTRIBUTION....
https://github.com/celphase/duck-pond/blob/main/src/synth.rs
To the credit of the author there is also an attribution file which describes a process of deriving the models from recordings (none of the techniques are very novel, but it's fairly impressive to see automated -- edit: I assume the project is LLM-generated) https://github.com/celphase/duck-pond/blob/main/ATTRIBUTION....