Why can my network camera stream be seen outside my LAN?

I’m using a network camera (IPCAM), connected by wifi to a Netgear (Nighthawk 8000) router which is behind a Comcast cablemodem. I just found out that on my cell phone, running the CAMHi app (made by the camera manufacturer), I can see the stream from the camera even though I’m not on my LAN (am far away, on Verizon network). I do not want the feature where I can access it from outside the house – I want to keep the data inside the LAN. I would have thought this is blocked by default on the router, but it seems that it’s sending ID info and a video feed back to the company mother ship. Is this expected behavior for such setups and what is the best way to block it?