You wouldn't have had to be online at the time. The virus database is updated automatically (unless you configured it otherwise), so if you had the faulty database it could have triggered an alert at any point, most likely if you ran an Avast! scan, or if you attempted to run the Tetris program.
I can tell you that during normal operation when Avast! moves a file to the "chest" it removes the file from the old location (so you still only have one file), but when it restores a file from the chest it copies the file back to the original location (so you have two copies of the file). You might still check the "chest" to see if the old files were deleted when you uninstalled Avast!
Beyond this I'm not really qualified. You'll need to wait for someone more knowledgeable. You might also ask this question at the Avast! forums -- they're a bit busy dealing with the fallout, but they would be the experts. The Avast! 4.x Home/Pro forum is <HERE>
Edited by Capn Easy, 03 December 2009 - 10:50 PM.