USENET very much depended on ISPs in practice, they ran most of the servers!
However, yes it was theoretically possible to have a route between two NNTP servers that wasn't over a BGP-routed chunk of internet but was "something else". Including posting a tape.
The last uucp service shutdown in 2012 according to wikipedia. So not just theoretically possible but was happening in actual pracitise much later than you would expect.
However, yes it was theoretically possible to have a route between two NNTP servers that wasn't over a BGP-routed chunk of internet but was "something else". Including posting a tape.