I don’t think it’s a particularly unreasonable request in itself, although I don’t know what your neighbours tone was when they made the request. Have you been downstairs to find out how noisy it is? We live downstairs from some people who don’t have carpets down and it sometimes sounds like a herd of elephants are upstairs!
Sounds like some discussion is needed to attempt to find a compromise.
PS. It doesn’t matter if they rent or not – an individual’s rights are not dependant upon their financial position or their home ownership choice.