Yeah I feel like something was definitely up with RDS, or at least this event is suspicious enough to warrant further investigation. Step one is definitely get all your "evidence" together - CloudWatch screenshots, logs, maybe cloudtrail etc. and then double check there's nothing you missed or any boo-boos in the scripts or data.

Either way, definitely mention your support interaction to your account manager if you have one, from how you've described it this was a pretty poor interaction especially if you're paying for Business support. If it's definitely not something you caused, I would also ask them to escalate the issue and get you an explanation as to why RDS did what it did.