Sounds like a great day.
"We then moved to a community center where we did some agete, some exercises where I was in seiza and Rob would put his weight on my shoulders. I would have to figure out how to move him."
This sounds like the triangulation principle my teacher does with me. In that if he is pushing straight on to your shoulders (or any where it really doesn't matter as the principle is the same) you form a triangle with your intent in order to "empty" his power and move him. [ie if you are standing facing each other and your 'attacker' has his hands on your shoulders, right hand on left shoulder left hand on right, then if you were to push directly into the attacker it wouldn't work therefore you focus your intent on any point on his arm and push there with you opposite shoulder. the effect is that one side of your body goes down the other up displacing his power and as your point of focus is also an empty point for his force he will be moved easily.] Is this what you were doing?
"One side.... down the other up"
This is a shear. FWIW.
"The empty place" = the right angle to the sum of forces in the effective lever arm -- which is also where you find the shear -- why your elbow tends to drop when you curl weights.