Alpha 0.0.0 is often grouped with other legendary "mystical" or "cursed" Minecraft versions:

: A version where every aspect of the game code is reportedly rewritten and unstable.

The Minecraft Alpha 0.0.0 glitch you're likely thinking of is related to a notorious bug that occurred in the early days of Minecraft's development. Specifically, this glitch involved the game's internal versioning system.

While modern patches have "fixed" the easy triggers, veteran users claim the glitch can still be reproduced on legacy launchers using the following method (accuracy not guaranteed by Mojang):