That's a good idea.
If the friend's USB factory cable does not connect, then there's something wrong with the head unit itself. I'm sure though your LG's factory cable should have transfer capability, not only charging as you said you tried it.
I don't want to speculate, but I offer you a personal anecdote.
I have a Samsung Galaxy S8 phone. Last winter I installed in my MK6 (2011) Sportwagen a Chinese-made Android 8.1 head unit that came with two USB cables. Well, I kept testing them with the phone to the point that it got me pissed and
had me "shouting" at the seller about the piece of "crap" they sent me... The head unit would just not see my phone. I tried almost everything possible since the phone cable is the factory one. I even downloaded an app called SmartSwitch in both, the head unit and the phone...Nothing. So I even ordered a
PC to PC Data Link file Transfer cable .
While I was waiting for that thing to arrive, I plugged in as a curiosity an older WD usb drive I've had laying around. The head unit recognized the WD drive right away. I ended up using mainly the Bluetooth function to listen to something I have on the phone.
I would think the factory-installed VW head unit is not as...fiddly as the Chinese unit.
Please update again when you have "news". The curiosity gets the best of me