Given the correct prompt, you can get the training set almost or completely verbatim [0]. Getting a GPL function is enough for GPLs virality, since you effectively lift the code from a GPL codebase and add to your codebase.

Plus, the stack's latest version contains at least one GPL repository which their license tool failed to detect. So it's not something hypothetical in the first place.

[0]: https://x.com/docsparse/status/1581461734665367554