Correct - but it does say nothing about using a VNC Viewer inside a browser. If you want to do so you do need additional software. noVNC is a good example: https://github.com/novnc/noVNC
It’s important that not the client is initiating the connection. For example: My VNC server is running internally and that’s fine, it should not be possible to connect to it from a public network (internet). Hence, HA (whose frontend is reachable from the internet) needs to take care about the connection. It has to act as a kind of “VNC Viewer Proxy”.