Not quite right, though very close. Correct definitions is this:
Default - your skill level slowly falls.
Capped - same as above, but it won’t fall lower than whatever its current level is
Int - same as first, but speed of skill rust depends on INT. INT higher - skills degrading slower.
Capped int - same as second, but it won’t fall lower than whatever its current level is
Really the system as a whole is fairly broken, and we’ve got an eventual rewrite pretty much planned out (it just needs to be implemented). For now I suggest capped int if you want to play with skill rust, it is probably the closest you will get to a balanced thing under the current system.