"Sorry, not buying that" is just brushing aside that they say they did exactly what you asked for.
They can say lots of things. I don't believe everything I'm told. Do you?
What is so unthinkable about producing compatibility with a file format that has a test suite?
Nothing - that's something I can believe.
Or cloning any particular feature from a high-level description and a screenshot of its dialog?
Any particular feature? No problem. The entire software suite function-for-function in just a few weeks? Without "cheating?" Yeah, that's a bit much.