It is not just the license, it is the ownership. For GCC or the kernel, that could mean the thing suddenly belongs to somebody and is not free anymore. Just remember the SCO and Java lawsuits and how they put a black cloud over things for a long, long time.
We will see how that turns out. I agree that consequences for Debian will probably less catastrophic technologically and may mainly mean they have to rip out packages or patches. Since anything contributed to Debian needs to meet the DFSG and hence Debian should likely be shielded against liability. The same works for the kernel where there are hard requirements that all contributions are GPL 2 and must be signed off by a human.
That said, the unclear legal status of AI generated code may place catastrophic liability on any contributor that was careless or lazy. GCC makes that quite clear, the kernel makes it less clear and Debian makes it somewhat hard to find out. Hence I think the main problem with this decision is that it endangers Debian contributors. Whether Debian has a moral responsibility here or not is up for debate. And I think that specific debate was mostly missing in Debian before the decision was taken.
That said, all technological advances carry risks and we just do not know. Obviously, it can still turn out that LLM code or LLM assisted code is bad enough that it will get thrown out almost anywhere and the legal question becomes moot. For example, there are some new results that it can make you code completely unmaintainable over a longer stretch.