I can confirm that either of the thunderbolt ports on the back of that dock can connect to a host machine. With mine, I connect a modern thunderbolt-3 mac and

I can confirm that either of the thunderbolt ports on the back of that dock can connect to a host machine. With mine, I connect a modern thunderbolt-3 mac and and older mac one with thunderbolt 2. I can leave both cords plugged into the dock all the time and just use the proper cable for the computer I'm using and it just works.