@alex relay.mostr.pub should probably return a NIP-02 contact list event (kind 3) that returns who users follow and lists wss://relay.mostr.pub as a relay.
mostr.pub doesn't appear to return anything when queried like:
{
"kinds": [3],
"authors": [pubkey]
}
this would also explain why mostr.pub users are listed as not following anybody in most clients.
i'm writing a tool that looks at your follows/followers and lists the top relays they use, and naturally, relay.mostr.pub is going to be missing from that list since it uses NIP-02 records.