As far as I understand, the argument is: it's impossible to learn human language from such poor stimulus without some kind of genetically determined universal grammar. If we prove that it is actually possible (even with non-human methods) to learn human language with such poor stimulus while not possessing a built-in universal grammar, that makes universal grammar unnecessary, or even contingent.

So, IF such a machine could be built, it would open the possibility that universal grammar, even if it exists, is only an accident of history (just as much as Indo-European influence on most European languages), not one of human genetics.