I had a similar experience with a company in Berlin, Germany. They didn't care about the code or my skills. Only if the submitted solution worked against their existing tests.
I think it's just a sleazy way of getting things built for free. Basically, write only a test for the functionality you want. And give the actual task to job candidates. If someone succeeds, you have both the algorithm and its test for pennies. It's based on P = NP. Testing the result is easy. Designing a solution is the hard part.
I now refuse both technical interviews and take at home tests. Limits my choices a lot. But the ones that remain are usually top shelf.