This a good design to limit the need to expose more than one HTTPS portsport.
Connections can be established by HTTPS but then converted into a simple proprietary binary protocol for speedy transfer of data.
No real value in using any standards like websockets since for a grid one is dealing with host to host communication. What ever is fast and simple. Can we eliminate the concept of server and client once connection has been stablished Not using websockets makes the protocol more symmetrical.
Once a connection is established, it’s a bidirectional pipe. This symmetry allows one to simplify the design.
See standard committees.