Pretty much everything exists in the training sets. All non-research software is just a mishmash of various standard modules and algorithms.

Not everything, only code-bases of existing (open-source?) applications.

But what would be the point of re-creating existing applications? It would be useful if you can produce a better version of those applications. But the point in this experiment was to produce something "from scratch" I think. Impressive yes, but is it useful?

A more practically useful task would be for Mozilla Foundation and others to ask AI to fix all bugs in their application(s). And perhaps they are trying to do that, let's wait and see.