Try the search yourself using inurl:viewerframe plus your camera’s make or model. Better yet, use and search for your public IP address. If your camera appears, your network is exposed.
The string you provided is a , a specific search query used to find exposed webcams and video servers. inurl viewerframe mode motion link
The "motion" wasn't happening on the internet. It was happening in his house. Try the search yourself using inurl:viewerframe plus your