His nonsense claim was that the TV would somehow connect to the internet through your Apple TV's wifi connection through the "ethernet" in HDMI. That's a completely separate bit of madness from the TV ...
Your TV's HDMI eARC port might actually be the best choice for your device, even if it's not a sound system, thanks to HDMI 2.1.
Learn how to enable enhanced HDMI on your TV for better picture quality with gaming consoles and streaming devices.