Streaming to a Broadcastify or any other server is a outbound connection so no, you don't need to port forward any ports. Port forwarding is only for inbound connections when running a server.
Nothing really special about port 80. It's a common (or default) port number used by public web(http) servers. If you were port forwarding port 80, no harm can be done.
Can you provide the link to what you read about port 80 so I can see what the author is saying.