Event ID 6009: is this event triggered only when a user-initiated shutdown has occurred?

Like the title says. From what I've briefly read, 6009 occurs when CTRL-ALT-DEL or Start > Shutdown is initiated by a user. If a shutdown sequence is initiated by SYSTEM for example, would this event also be logged?

Event 6009 is logged at startup, not at shutdown. It contains only a string identifying the operating system version. It's been that way since NT 4.0 or so.

If you're looking for a system initiated shutdown/restart, look for event 1074. The details for this event will tell you what process initiated the restart and what reason was given, and you can check the reason code for further information about why the system shut down or restarted.