That claim isn't surprising even if it came from a company with no vested interest.

Most people who have those smart devices aren't really in the technical field. They won't have VLANs segmenting their network, or sniffers watching, let alone a proper firewall.

Look at Mirai; took over smart devices and instead of gaining footholds into everyones network; just used all the outbound traffic.

I wouldn't dismiss the claim just because an AV company said it.