LG very likely has your neighbor's WiFi password, so even if you don't connect it to your own network, they could theoretically just try and connect to any known network nearby. No 5g modem needed.
Idk if they do that, but it doesn't seem complicated to implement, and it doesn't seem to fall outside of the company's ethical boundaries.
For now, it remains easy and sufficient to not give them your wifi credentials.
People need to stop pretending there can only exist a single hardware/software configuration that also never changes.