Nah. They could have just overprovisioned to hell for much cheaper. Boxes at Hetzner cost up to 10 times less than equal level of AWS compute. Just overprovision for cheaper. You have to overprovision on the cloud anyway - you cant risk your users waiting 1-2 minutes until your new nodes/pods come up. So 'cloud is good for spiky load' argument is just a lie we tell ourselves.
Well in cloud you do over provision a bit by setting autoscaling rules in a way that you still have spare capacity while the new resources are bootstrapping.