by definition?

the Free Software Foundation, the ones that started the whole idea of sharing code as a philosophy of software, do not consider source available as free software or “open source”.

It does not meet Eric S Raymond’s definition, the one who invented the term “open source”.

It does not meet the Open Source Initiative definition either.

Even Wikipedia gives the right definition of open source:

They grant the recipient the rights to use the software, examine the source code, modify it, and distribute the modifications.

So stop defending Rossmann and admit that the app is not open source.