Tesla User Experience Designer interview questions

The recruiter I worked with was really nice and gave me a lot of tips on what the designers were looking for, and the designers that interviewed me were very insightful and down to Earth. Pretty much just presented one of my projects and picked my brain. I was then given a 1-week design challenge, and didn't go past it. Overall it was a great experience though.

The first round was portfolio presentation, and it ran smoothly. A few hours after interview, the recruiter reached out to me and said I made it to the 2nd round, which is take-home design challenge. It was fine to me, since I know that most take-home exercise normally would require less than 10 hours to complete for respecting candidates' time. However, when I receive the topic, it started making me feel so uncomfortable: 1) The topic is vague and requires lots of background knowledge, it is impossible to complete it within 10 hours, and the recruiter even encourage me to spend as many hours as I want. 2) The topic is related to the Tesla product, and ask me to provide an end-to-end solution for one of their existing products. Making me feel it is a free work for them. 3) Based on the document they provide, the project that I created would own by Tesla once I submit it, I can not even post it on my portfolio site. The question is if company worries about the NDA, why you choose a company related topic? However, the recruiter keeps pushing me and encouraging me to work on the design challenge, said I was the most fav candidate by the team. So I ended up with spending more than 40 hours on that, which proved was a wrong thing to do. Once I submitted the project and provided it with the recruiter, he just disappeared and a few days later, he comes back to me said I was rejected because my design doesn't match with the team, which I really don't understand what it means the design doesn't match with the team? this is the only feedback that I got after I spending 40 hours on the project ><