My professor was definitely a good professor and no way they would have done that. It clearly would have been done as an added challenge for themselves for fun and there's no reason to penalize that.

It's definitely fun: you can also take part of the challenge to be figuring out what parts of the full language are worth adding to make the overall job easier (so you're not taking the language subset as set in stone). When I did this for Python I started out in unrestricted Python, gradually both increasing what's implemented and reducing what's used. (Result at https://codewords.recurse.com/issues/seven/dragon-taming-wit...)

I doubt I will ever be a professor, but I would be happy to pass any student who did this provided they did the task adequately. Maybe extra points for cheekiness.