He went a bit overboard

My husband and I have always been on the same page when it came to disciplining our kids and if either of us didn't agree with a particular punishment, we'd usually discuss it together, privately and make corrections. Today we were all at Wal-Mart, all 7 of us, he went in one direction with the big kids, I went in another, with the baby. Anyway, like most kids our preschooler is high strung, even worse when he's tired and since he hadn't slept at all last night, he was pretty tired, so he was overly excited, then whiny. Apparently, my husband had spoken to him a few times by the time I caught up to them in an aisle. Our daughter had a toy or something and she didn't let him have it when he asked, so he started whining and as he was about to complain to me, his father reached out and hit him on the butt. Now, it's not the smack on the butt that pissed me off but rather, the fact that he hit him hard enough where he fell against the shopping cart, then hit the floor. He started crying and holding his knee. At this point my mama bear claws came out and I reached for my son. As I made my way to pick him up, my husband goes "relax, you don't know how bad he was being the whole time", I told him he didn't have to knock him to the ground and I called him to me. My husband reaches out and grabs him by the collar and picks him up, putting him in the cart. I was livid but I didn't wanna make a scene in front of the kids and in walmart, so I walked away. He got mad and I saw him storm to the check out line, pay and leave the store. I had to put everything in my cart back as I didn't have any money on me. We discussed me forgetting my wallet on the kitchen counter on our way to the store, so he knew I was depending on him to pay. We haven't spoken since and he has an attitude like I'm wrong. Sorry it's so long! I'm just so aggravated because he's walking around with a bad attitude like I fucked up. What do y'all think?