No, it sounds like she was quite out of line. I think you need to call her or go to her house, or mail a letter, whatever way you think she might actually hear you best, XXXXX XXXXX her know that your husband was not trying to criticize at all. Let her know what your husband's intention was. Have your husband apologize for doing something that offended her, if he is willing (he did not do anything wrong, but he did hurt her, he can apologize for doing something that she perceived as hurting her and her son).
Once you have things sorted out, talk to her and let her know how hurt you and your husband are. Explain that you feel you should have been given an opportunity to explain yourselves, that you and your husband have spent a great deal of time with your grandson, and that mistakes are bound to happen when you spend so much time together.