If they did that you would see the cable, they would have to somehow break into your house and route a cable from your router. I've never heard of anyone doing this, it just isnt practical.
Just because you see IPs that aren't your computer doesn't mean there's an issue. That scanner will show PCs, phones, tablets, set top boxes, smart TVs and even more things that you probably forget are connected to your network in some way. I mean, nowadays you can get network connected lightbulbs!