A combination of username, steamID and display name completely understandable in my opinion. User shouldn't be forced to login using a randomly generated ID, but something he can remember and has the option of being private by being able to use the display name.
UrlID can be beneficial for the user so the user can choose a easily spellable identifier for the URL in case he needs to share the link often using voice.
Seems like an optimal system except that the UrlID probably is only a use case not that often. But it still won't really hurt anyone. If it wasn't the URL ID it would be steamID, which does nothing to help to remember the URLs. So why is it poorly thought out if it gives benefits to some usecases without making anyone else worse off?
1. Username, used to login, not visible elsewhere, unique and security related.
2. SteamID, id number which is visible elsewhere and used in their api fairly often; not too different from the username other than being public
3. UrlID - by default a "steamcommunity" link to the user's page is their SteamID, but it can optionally be edited by the user to a custom url. This ID is a globally unique namespace. For example, https://steamcommunity.com/id/gaben
4. Display name ... Yup, the display name. Arbitrarily editable.
Having that many things is dumb. Having an editable url component is dumb (it shoulda just been the steamid forever).
All in all, they're not a good example.