I think you did the right thing. I am getting so frustrated with people telling me my writing is wonderful. I have poor grammar and I know this. If I put something on Amazon and it had a lot of errors I would want someone to tell me. I had a friends wife edit one of my stories for me. She has a masters in English. I found so many small errors in my story after she edited it. What if this person paid someone to edit their book and didn't realize the person did a poor job. When you have bad grammar its hard to know if the editor knows what they are doing. I think you did the right thing.
the question is if this view would be universal, especially whrn the crit came unsolicited.
OP, I think you got very, very lucky. You could very easily have acquired a reputation, instead of a beta.