Grounding a 6 year old: Did I do the right thing telling my ex and his new wife they need to come to me before making big decisions like this?

My daughter came home from her dad's tonight. I haven't seen her since Friday morning, but we had little FaceTime talks since then. I picked her up after school and she told me how she was "grounded" over the weekend "but I couldn't tell you until today"(red flag? I think so...but anyway). I asked her why she got grounded because her dad and her stepmom said nothing to me about it.

The story I got from both my daughter and my ex is that she didn't come to dinner right away on Friday, so she didn't get dessert and was grounded all weekend. My ex says this is an ongoing issue with her where she "ignores them". My daughter said she doesn't ignore them. She just can't hear them if she's in her playroom and they're calling her from across the house.

I asked my ex about it and his story completely corroborated hers but he says that "she should know when dinner time is". I asked him how she would know when she can't tell time and he said "it's the same time everyday. She gets to school on time". I said yes, but we make that happen. What do you do to make sure she comes for dinner because let's face it, she can't really tell time.

He and his new wife said they got her a watch. I said that's great but she can't tell time. Do you have a timer set that goes off when it's time for dinner? If she says she can't hear you across the house, do you walk over and tell her it's time for dinner? I told them that I feel like they didn't give it a fair chance before jumping right to grounding her. They said I'm coddling her and siding with her which undermines their parenting. I asked them if they've ever stood in her playroom and had the other call from the kitchen and they said "Hailey needs to come to the table the first time we call her." Which to me means they have no clue if she can hear them down in her playroom or not (which is a whole other issue because if she calls them and they can't hear her, THAT'S A BIG PROBLEM!)

I told them that I don't think they took the right steps with this. I don't have a problem with getting my daughter to come to dinner.

They asked what I would do and I said well first I would ask her why she can't hear me calling for dinner and then I would make sure I could hear someone calling from the playroom. If I can't hear someone calling, then maybe our daughter can play in the playroom until 15 minutes before dinner is ready, then someone can physically go get her and have her help set the table and be in the general kitchen area. I didn't think this was too much of an ask but ooooooh buddy..... You think I'd told his new wife she needed to shave her head.

I told them they need to set realistic expectations but not just dismiss our daughter. Giving her a watch is great, but it's useless if she can't tell time yet.

I told them in the future, let's work together to come up with fair rules to follow and reasonable consequences. They just left me on read. I hate fighting with them but I feel like this is just common sense too.