Was the Dynamo outage separate? My take was the NLB issue was the root cause and Dynamo was a symptom which they flipped some internal switches to mitigate the impact to that dependency
If their internal NLB monitoring can delete the A record for dynamodb that seems like a weird dependency (like, i can imagine the nlb going missing entirely can cause it to clean up via some weird orchestration, but this didn't sound like that).
