When you perform quick backup, Veeam Backup & Replication creates a single VM incremental restore point. Unlike a regular incremental restore point that contains data for all VMs in a job, single VM incremental restore point contains data only for a specific VM.
A single VM restore point is not regarded as full-fledged restore point in the backup chain. From the retention policy perspective, single VM restore point is grouped with a regular restore point following it. When Veeam Backup & Replication needs to delete a single VM restore point by retention, it waits for the next regular restore point to expire, and deletes two restore points at once.