To clarify, supertux2 is mostly a distro thing. For a while both 0.1 and 0.3 were shipped, and the user-made levels were not quite compatible between them.
Specifically, 0.1:
* had a fixed screen size
* only let you go forward
* used different mechanics for the fire-throwing upgrade
Nowadays it's been long enough that most levels are written for the later versions. And IIRC recent versions re-added some support for forward-only levels (race against the clock).
But yeah this has nothing to do with the actual content of the levels, it only refers to the engine.