Non-WiFi devices can interfere with all devices, not just hot spots - true. But that does not mean you want your hot spot interfered with. 5 GHz would reduce such interference and an ethernet cable would eliminate the possibility.
Lists various sources of interference
https://support.apple.com/en-us/HT201542
Regarding other WiFi networks:
How You and Your Neighbors Are Making Each Other’s Wi-Fi Worse (and What You Can Do About It)
https://www.howtogeek.com/209450/how-you-and-your-neighbors-are-making-each-other’s-wi-fi-worse-and-what-you-can-do-about-it/
The above article does not address the Wi-Fi media access protocol, which can minimize interference, but not eliminate it completely.
Anyway - bottom line: We can argue as to the potential impact on one WiFi network on another, but considering all the other sources of interference, 5 GHz and cable options would be desirable.