Err, what :?
Code:
Update_kindle_3.1_B006/Update_515460094-558700031
Code:
Update_kindle_3.3_B006/Update_525120101-611680021
Looks sound to me (The 3.3 update actually needs at least 3.0.something!=0, not necessarily 3.1), and the files haven't been touched.
You sure you don't have a hack messing around with the prettyversion.txt file? (Or that Amazon just slipped you the 3.3 update OTA?)