AITAH for mansplaining breastfeeding?

My wife and I have an eight months old. For various reasons, we are not feeding him baby food. We eat meals together as a family, and in addition to breastfeeding he has access to what we eat (usually eggs, avocado, tofu, salmon, steamed broccoli, lentils, etc…) We let him choose what to try or if he wants to try anything at all.
My sister has been saying for two months that our baby needs to eat baby food, but that simply isn’t true. Our pediatrician said babies can be exclusively breastfed for up to a year. We got into an argument about it yesterday, and my sister said babies need to have baby food introduced to them at six months, that they can’t skip from breast milk to adult food without that crucial step. I told her that she is wrong and they can. Our baby eats eggs quite happily. She said babies shouldn’t eat dairy before a year. I said eggs aren’t dairy.
My sister got really frustrated during our argument and asked me if I really thought that I, as a man, understand breastfeeding better than her. I said that I do think so, because I’ve been watching my wife do it for eight months, and my sister doesn’t have kids. I also said it doesn’t matter if my sister is the world’s leading expert on breastfeeding, because my wife and I are in charge of how we wean our son, not my sister. She doesn’t get a say.
My sister said she couldn’t believe I had the balls to mansplain breastfeeding to her. I said to believe it, and she didn’t like that. Am I the asshole? I feel like she should keep her opinion to herself.