Close, but no cigar. You're definitely right that you want the weight of the stand over a leg. If any of you reading this don't believe me, take a c stand and fully arm it out over the big leg. Push down, and watch nothing happen. Then rotate it 180 degrees so it's in this bullshit angle of view thing the OP suggests. The part where you're incorrect is in the "opposing weight" myth. Doing the same exact process, but placing a bag on the big leg, will demonstrate that weight over the big leg (with a sandbag on that leg) will always be the safest method.
Except that guy is totally wrong and doesn't understand basic physics. That "key grip" shouldn't be trusted with set safety if he can't set a c stand right.