I think the huge proposal (after several rounds of questions) was what sunk him. The instructions did not request a proposal, and submitting one, especially one that detailed, conveyed “OP cannot take the initiative and proceed with work without seeking approval beforehand.” The project was about asking a few questions, listing a few assumptions, and giving yourself approval to confidently dive in and build something ambiguous. Maybe I’m wrong, but I don’t think the code mattered after that email was sent. The company should have just ended it there without him wasting his time building the assignment.