The updates directories each contain a file named "state":
https://dl.fedoraproject.org/pub/fedora/linux/updates/27/state https://dl.fedoraproject.org/pub/fedora/linux/updates/28/state
But the F28 one seems quite stale, having last been updated on April 26th. The F27 and F26 files appear to be up to date.
This is a stale state file from pre-GA, the correct ones are in /Everything and /Modular, since those are two distinct composes.
The updates/28/state file is now gone. Thanks for the report.
updates/28/state
Metadata Update from @puiterwijk: - Issue close_status updated to: Fixed - Issue status updated to: Closed (was: Open)