Bright Crowd Machine Learning Engineer interview questions

I applied online and got a reply with a coding challenge with their company's real dataset. I was asked to solve it within 24 hours and submit it along with a writeup. I analyzed the dataset very well but I got a reject within few hours of submission. I highly doubt that these guys made me do their work for free! And the best part is, a person with non-ML background reviewed my analysis and ended up giving me suggestions about the same, when everything I did was perfect and I am very confident he didn't understand how I analyzed it at all!