Just like Lin Xiao's school, Level One High School certainly has public Divine Realm Login Cabins, but unlike personal exclusive Divine Realm Login Devices, in addition to entering one's own Divine Realm option, there is also a local network option that allows entry into the local network of Level One High School, which is to access a public Divine Realm unique to Level One High School.
Actually, the Divine Artifact Platform that appeared during Lin Xiao's final exam was a small local network, accessible only to those with permission.
The local network at Level One High School was a small void city situated in Subspace, only accessible by students of Level One High School and limited to enrolled students; students could not enter it when they were on vacation at home. Therefore, when Lin Xiao arrived on a massive platform, aside from their group of seven, there were only a few distant figures drifting by, presumably students or teachers who were still at the school.