Lazily loaded would refer to the fact that it's only loaded when needed. In other words, when he restarts the server, he doesn't load up any data for the users. Instead he just creates a reference to the filename that contains all the user info and creates a data structure to hold all that info in. Then, when someone attempts to login, he searches through the file and finds the credentials, and if successful pulls all of the users information into memory.
Before this change, he stored the information for all users in memory, even the ones who no longer use the site, as soon as the server restarted.
Almost, but it's not only at login that you need user data.
Basically I changed the code that looks up stuff about users (formerly just a hash table in functional position) to call a function that loads a user from disk first if necessary.
Before this change, he stored the information for all users in memory, even the ones who no longer use the site, as soon as the server restarted.