This was not an interview, but the interviewer’s self-assertion by humiliating the candidate. The test itself is not aimed at identifying your experience or depth of knowledge, but simply whether you can code quickly.

After the task, there were comments like:

• "Yes, your level is definitely not up to the level of Revolut."
• "You position yourself as a Senior, why don’t you have developed live coding skills?"
• "Knowledge in testing is rather weak."

How did you manage to understand this on some elementary boilerplate cases that are usually not written by hand?

There were no questions at all about the intricacies of multi-threaded processing, atomicity, and asynchronous collections that the recruiter spoke about. There were no Senior-level questions either.

This is just a simple project to complete. Read the Android Recommended Architecture article and an article about Clean Architecture on Wikipedia, and you will manage.