Just as the most obvious example, several large GPL libraries, parts of GCC such as libgcc, and more, run under the GPL linking exception -- this exception to GPL-licensed libraries means that programs using those libraries directly are not subject to the rules of the GPL, while normally they would be (under the "derivative work" logic). For example, every C program compiled by GCC links against libgcc, which is GPL. But you are not implicitly put under the terms of the GPL, just because you used GCC to compile something, and it happened to use libgcc. libgcc explicitly exempts this use case.
So, why does this exception exist, and why is it explicitly stated? Precisely because, just like those "template content libraries" from some random vendor, GCC links your code against components and libraries that have clear licensing terms. The licensing terms of those libraries absolutely impacts the licensing terms of the final, produced work, unless stated otherwise. (Have you ever noticed how even commercial software is required to maintain a copy of the BSD license? Well, it's legally required to, if you use BSD software. It says so, right on the tin.) This isn't some kind of legal 12-dimensional chess, it's a fairly obvious bump you encounter quite quickly. This is obviously especially important for compiler-style things, since in reality, their whole purpose is to generate "derivative works" of all sorts. Guile also has a GPL linking exception for some similar reasons, IIRC.
In all honesty, to me, the weird thing about this case isn't that they're making claims about "derivative works" or whatever, with regards to libraries. It's weird to me that they even need to make the argument at all -- most of the time, with a lot of software, the licensing situation surrounding components like this (and how you can use them) is pretty clear. It seems odd it wouldn't be strictly clear already, in a way.
So the issue remains if they knew the wendir hadn't a license - that'd be necessary to know where to assign damages, but still they would not be able to use the output, as created without a license to begin with.
If the vendor had not a license to work with the software the output has been illegaly obtained, while claiming copyright on the output may not stick claiming a royalty along punitive damages is not that far fetched.
I wonder if these templates came with a license, or are considered part of the CAD software and not redistributable?
And electronic engineering work is derivative of physicists' work.
And physicists' work is derivative of mathematicians.
And mathematicians's work is derivative of Colombian coffee farmers.
And mathematicians's work is derivative of pharmaceutical companies that produce amphetamines
And pharmaceutical companies that produce amphetamines are derivative of chemists' work
And chemists' work is derivative of physicists' work, which gives us a nice loop
Doing anything else would result in exactly 0 users.