Presumably they mean that the CPU resources are over-provisioned, meaning that the virtual CPUs allocated to VMs have to share a smaller pool of physical CPUs. If the VMs have a lot of idle time, this can work well, but if your VM suddenly needs more CPU, the processes on your VM might need to wait for a physical CPU, as physical CPU cycles that would normally be available to you have been “stolen away” by processes running on other VMs.
Presumably they mean that the CPU resources are over-provisioned, meaning that the virtual CPUs allocated to VMs have to share a smaller pool of physical CPUs. If the VMs have a lot of idle time, this can work well, but if your VM suddenly needs more CPU, the processes on your VM might need to wait for a physical CPU, as physical CPU cycles that would normally be available to you have been “stolen away” by processes running on other VMs.