LOL no you're certainly not 'stupid' I run into the same problems all of the time, trying to figure out how things work.
I see what you're saying about the pin 85 on the heater. In the diagram, it shows that pin to connect to the output wires on the Maxy and it can use either one: Output 1 [yellow L10] and Output 2 [grey L5]. Once the Maxy sees a low pressure on the bottle, it grounds either output, and in this case, it would ground the relay to power the heater. That's why the wires for the ground on the Maxy are so beefy: it can handle a lot of power. You can use the outputs for any number of accessories besides a heater.
I hope that explains well because I'm HORRIBLE at explaining things.