As I understand it, a "reboot" means you throw all or nearly all of the character's old continuity out the window. If you simply rearrange certain details of his "ancient history from many years ago," that's just a garden-variety "retcon."

When John Byrne's "Man of Steel" mini started coming out after "Crisis on Infinite Earths," it was a Superman reboot. Because just about every story ever published about Superman in previous issues of his various series ("Superman," "Action Comics," "Superboy," etc.) was being thrown out the window.

On the other hand, when Mark Waid's 12-part "Birthright" came out several years ago, it wasn't a reboot. It was just retconning various details of Clark Kent's childhood and his first months on the job as a costumed superhero after he started wearing the colorful Superman outfit.

But the underlying assumption was that, aside from the details of his backstory which were being rewritten on the fly, nearly all of his previous Post-COIE stories were still in continuity. For instance: He had still gotten himself killed in the stories of the early 90s, been "replaced" by four different guys with S-shields on their chests, and then finally came back from the dead. He had still married Lois Lane after a long engagement; he had still experienced the horror of seeing Lex Luthor get elected President of the United States later on; and so forth!

As far as I know, "Secret Origin" is going to be more of the same. It will, once again, give us someone's "new spin" on how Clark Kent became the Superman he is today. But I don't expect it to tell us that most of his published stories from the last 23 years or so are now being "erased from history!" That makes it a retcon instead of a reboot -- if I'm right!