Thanks to both of you for this info! It all makes sense, as I couldn't really see anything that would "tell" the system that anyone was or was not in the passenger seat.
When my passenger seat is out, I have a plywood box in place of it (bolted down to the seat mounts), and the top of the box is just slightly below the level of the top of the console. I don't plan to have anything any taller/heavier than a map sitting on top of the box when underway, so there will be nothing "in the path" of the airbag to potentially fly around. And of course with the seat in, all is similar.
Whew, now I can never get a newer van because I'd have to learn a whole new system