It’s doubtful in my opinion that APKPure is on sound legal footing. Nor would this square with even their legally dubious terms of service. https://apkpure.com/terms-service.html
Its also interesting that api.cleanapk.org is shrouded in such mystery. Even though it occur’s in the source code in what is supposed to be a highly transparent project.
It also sounds like it’s likely not going to be addressed by any explanation should would materialize. Even though it clearly is in the sourcecode.