Interesting, in which language Damián is written this way? I only know one.
“one connection per user” means exactly that, one connection per /ppp secret item. So if two devices attempt to connect using the same credentials, the second attempt is rejected.
To link static interface names to user names only makes sense when you need specific firewall rules to be used for the clients.
If you intend to have several devices connected from behind the same public address at least once in a blue moon, you’ll have to bite your way through this article.