This API is generated by generate-it.
See the generate-it docs: https://acr-lfr.github.io/generate-it/#/_pages/cli
Put simply, this tool takes an asyncapi or an openapi 2 or 3 file and output code via a template hosted on github.
To see the dummy API working you will need to download https://github.com/j-d-carmichael/api-dummy_d the accompanying openapi repo next to this repo in your local directory tree.
With both downloaded, run the npm script "generate:server".