Girls I need some serious advice about my MIL

Please be prepared this is a Very long story about my Mother-in-law. So to begin my husbands parents are divorced, and have been for quite a few years now, after my MIL separated my Father-in-law she started dating his best friend. My husband isn't okay with the relationship and has never supported it, she's tried to change his mind but he thinks that it's wrong and a slap in the face to his family because he was like an uncle to him growing up. He's made his feelings very clear to her and for this reason he's said that he won't be around him when he's around we came to an agreement about holidays and she recently broke that agreement and excluded us from Thanksgiving, by choosing to have him go with her to her sisters house. They recently became engaged just before Thanksgiving, and my husband has made it clear he's not going to the wedding. This lead to some gossip about my husband at Thanksgiving which has gotten back to us. 
Fast forward to today, my MIL came by our home to drop something off my Sister-in-law I walked outside to get the mail as she pulled up I said "Hi" and waved and went back inside and told my SIL that she was here. My husband gets off work and has a text waiting from my MIL for him to call her, which he does after talking to me. I said off the cuff jokingly it's probably because I saw her today and didn't stop to have a conversation with her all I said was Hi and went inside. He asked why I just went inside and I further explained that I had no shoes on, it was fairly cold and windy out, and I had to use the restroom as well. He told me it was no big deal and I had done nothing wrong. 
So he calls her after getting off the phone with me and she proceeds to say I was extremely disrespectful to her that she's his mother and doesn't deserve to be treated that way that I went out of my way to ignore her. He then stuck up for me which lead to them having an argument about how she treats us. 
When my husband calls me back he is upset, he had a very long day and didn't want to deal with the drama. He told me what happened and how she blew everything out of proportion and it has me sitting here in utter disbelief that this all spiraled out of control this way. I don't feel as if I did anything wrong, and I don't think that I even gave off a bad vibe at all. She wasn't there for me and I was preoccupied with what I was doing and needed to do. I was just getting the mail real fast and get back inside because it was windy and cold, I wasn't trying to start any drama. 
So I guess my question really here is did I do something wrong here? How do I move forward from here?