I don't know if this is the origin, but the semver spec says 0.x.y is unstable. Sure, not everybody uses semver, but it is popular enough for people to make incorrect assumptions.

https://semver.org/#spec-item-4

It's not the origin. Using 0.x for stuff like this was already a thing long before semver. For example, the very first release of Linux in 1991 was v0.01.