It's really odd seeing Chinese companies taking someone to court for IP infringement given that that is the modus operandi of Chinese companies and has been for decades.
The PRC started enforcing US/Berne copyrights quite seriously for big companies 5-10 years ago, after negotiations with the US under the Obama administration. They actually licence, buy, or invent huge amounts of IP today, straight rip-offs in China now are mostly just small time hustlers on Alibaba that everyone hates. For example, Huawei spends gigantic amounts of money on R&D, equivalent to Apple and more than Samsung.
Part of those negotiations would have been that China is not unfairly excluded from being able to own IP and prosecute others for the same laws it was agreeing to be subject to.
Nothing weird about it, has also been part of their MO for a long time. If a Chinese company infringes it's okay in their mind cause they have to "catch up", but if they can use it to go against Non-Chinese companies: Bring it on.
https://github.com/Freetz-NG/freetz-ng/discussions/134 is the first I could find re getting the sources. Note, that the GPL requires the sources in "the preferred form" and that includes a way to build them (if AVM has a way to build the sources, which they certainly have).
Last time I got (or a customer had) a AVM box I requested the sources and got nothing that could even build (invalid C files, AFAIR).
Part of those negotiations would have been that China is not unfairly excluded from being able to own IP and prosecute others for the same laws it was agreeing to be subject to.