“Persistence” in the loki helm charts just refers to the way that data is stored on disk. In the Loki helm chart, Loki is run in a k8s StatefulSet and the URL you’re pointing to inside of values.yaml just controls all the aspects of how the helm chart saves to disk.
I suspect because you’re mentioning S3 though, this isn’t actually what’s interesting to you. Inside of Loki’s config (rather than the helm chart config) you can find options for storage_config which includes use of S3-compatible APIs with boltdb_shipper. Check this page for more details:
It’s important to read the top parts of that page to disentangle what “storage” is from “persistence”. At the helm chart layer, the kind of persistence/storage concerns you’re seeing are not the same thing