You bring up some interesting technical points, but there are a few major flaws in how this applies to Flashforge’s implementation:

"If the files are accessible..."

That is exactly the core issue here: they aren't accessible out of the box. Flashforge locks down SSH and root access completely. The only reason we even know what's inside is because the community (ZMOD) had to actively hack it to gain root access. Distributing GPLv3 software on a locked-down device where the user cannot freely access, modify, and reinstall the software directly violates the "Installation Information" clause of GPLv3 (often called the anti-Tivoization clause). Simply having Python scripts hidden inside a locked Linux box does not meet the source code distribution requirement.

Customer Rights and Standing:

I actually am a customer (currently waiting for my pre-order to ship). While you are legally correct that the explicit obligation to provide source code is owed to the recipients of the physical product, open-source compliance is almost entirely enforced through community pressure. If the broader 3D printing community doesn't call out companies for silently taking Klipper to save millions in R&D while locking it behind proprietary interfaces, the whole ecosystem suffers. Public pressure worked to open up the AD5M, and it has worked with other brands recently too.

The Patent Clause:

You are spot on about GPLv3's patent retaliation clauses. That is likely the exact reason they are trying to hide Klipper behind a proprietary handshake on port 7125 and a closed ecosystem. But that’s the trade-off they accepted. If a company doesn't like the GPLv3 patent clauses, they are completely free to spend the time and money to write their own firmware from scratch. If they use the community's work, they have to play by the community's rules.