I changed wording of the quote a bit, so it would match your question.
When you connect to a client, you will receive responses on the port
you just used to connect to that client. The Bitcoin network uses persistent TCP
connections that remain active so long as both nodes continue running.
Bitcoin communication with non-standard ports
For the sake of discussion we can define Server as the side that waits or listens on port 8333 and Client as the side that initiates connection by sending network packet to "server_ip_address":"8333" , the network packet has address of the Client, so Server can send reply back to "client_ip_address":"any_port_reserved_for_client_on_client's_network" .
Bitcoin always reserves 8333 port on workstation to communicate with Bitcoin Network, but usually home router changes the port number in packet when it's on it's way out for the Network Address Translation mechanic (NAT). To overcome NAT and make Bitcoin Client act as Server and accept incoming connections, Port Forwarding or UPnP should be enabled.