The whole point is to get the game engine version, so that a mod can have different behavior based on the engine version (to work around bugs, for instance).

0xabcdef 20 Sep 2017:

Should rename getAPIVersion to unvGetAPIVersion and make it return the game API version. Extension API version is still accessible by typGetProperty.

george moromisato 23 Oct 2018:

In 1.8 Beta 4 I've added (unvGetProperty 'apiVersion), which will always return the API version of the engine.