There is a difference between privately browsing something and using a VPN. A VPN is something that you rent for money or install on a VPS, not everyone gets it. A VPN is mainly used to encrypt your browsing so that no one knows where you are from or what your details are ( ip etc). The private browsing thing in your browser has nothing to do with a VPN, private browsing just doesn't store any information of the sites you visit on your PC. PTA can still tell what you are watching even if you are 'privately browsing' the web using your browser. But if you use a VPN, they wont find out anything you do on the interent, you are invisible to their eyes.