As a part of an interview process, I've been asked to solve a take home challenge. Before I can access the data, I've been asked to sign a NDA. The NDA is generic stuff which says everything belongs to the company, etc. etc. What is curious to me is that throughout the contract, I'm being referred to as a "contractor". Is that normal? I'm not being paid or compensated in any way to solve this challenge.
I'm not being paid or compensated in any way
Yes you are - you are being given the opportunity to be considered for a job. This is valid consideration (compensation) under contract law.