AITA for snapping at my mom?

My wife and I have 2 kids. M6 and F2.

Last weekend was my birthday and my wife planned a trip to a nearby town with my family.

She told me to just enjoy myself and she will handle everything including the kids.

The house we were staying in had a pool. We told the kids not to go near it.

I was spending time with my cousins and suddenly someone was yelling saying my son fell in the pool. I jumped after him and saved him. He is fine now.

Apparently my wife told the family to look after our son while she fed our daughter. They got distracted. He ran by the pool and fell inside.

My wife was feeling terrible and kept apologizing saying she should have been more careful. My mom started yelling at her saying she almost got him drowned and called her a terrible useless mom.

I got upset and told my mom to either shut up or get out of there.

Could my wife have been more careful? Yeah but so could I. I refuse to let her take all the blame when I was having fun instead of parenting. Also where was everyone else? Why was no one looking after the kids?

My mom thinks I'm an asshole and shouldn't talk to her like that for a "normal reaction" to having her Grandson almost drown.