The green is your primary tank (most forward on the chassis) and its air goes priority to the rear air brakes, then the front suspension, etc. The red needle reads pressure from the secondary tank whose air goes priority to the front brakes, then rear suspension, etc. When you first start up, the green needle should move up ahead of the red.
The secondary tank gets its air off the dry side of the primary, which is why its needle follows the green one up. It would, therefore, seem unusual for the red needle to show more pressure than the green. There must be a broken air line associated with the primary tank, but allowing engine compressor air to pass through and pressurize the secondary; so hopefully the tow truck's pressure will be enough over the lost air rate to keep the parking brake released (its relayed air comes from the primary tank).
Your braking was spongy because the primary supplies rear air brake pressure; it's likely most of your braking to get off the road here was by way of the front brakes.
Joel