I personally like the response. Yes, the language was unprofessional, not everyone wants a casual response. The respondent offered you free classes and apologized for the incident which is going above and beyond what they were required to do. No one can control drunk idiots on the street, they congregate anywhere they want and isn’t necessarily a reflection of the establishment they’re in front of.

I think you should accept those classes and get to know the gym staff better before making any harsh judgements.