Low tire pressure causing fall in corner?
I presume you were riding in the direction you came across the bridge and down the ramp.
I doubt tire pressure had anything to do with it. On a moutain bike sized tire, unless rolling tires of rims, too low tire pressure tends to cause imprecise handling and a general 'sloppiness' in the front end. "wiping out" as you did is not typically caused by low pressures.  Check the rim for scrapes that would indicate you rolled the tire off the rim and had the rim hit the ground. 

The weight on the back of the bike, and the change in angle that coincides with the corner probably unloaded the weight off the front wheel. The amount of friction you get is directly proportional to weigh, so the wheel 'wiped out' from under you because it was not far off hanging in mid air.  

When learning to mountain bike one of the first skills you need to learn is to load the shock before the corner and maintain pressure on the front wheel though the corner, letting the shock do its job of maintaining wheel contact with the ground. In this case if you had loaded the front shock, the change in angle coming onto the ramp would have be absorbed by the shock as it extended to maintain wheel contact pressure with the ground. 

Things that could contributed to the crash are rider position - too much weight too far back into and though the corner. This means not enough weight on the front wheel to maintain traction and not enough preload on the fork for it to hold the front wheel on the ground.  The solution to this problem is enter the attack position, move body weight forward (not lean) to load the front fork with plenty of weight to hold the front wheel down.  With 30kg on the rear, there is very little risk of putting so mach weight too far forward you go over the bars. Just how far forward you can go is much further than most people think, and is very unnerving for a novice until they have practiced doing it many times.  

The other thing that could easily contribute to the crash is the fork settings - damping, rebound and air pressure are all available on the Reba. Getting this set correctly will make a big difference to hold the front wheel on the ground. With these set correctly, maintain a good weight distribution with you body well forward becomes easier as you learn to trust the fork to work for you. With these set wrong, the fork can feel like its working against you and you are less included to load it. 

All that said, the speed you went though the corner with that bike setup and weight was fairly ballsy, and the outcome not entirely unpredictable. If you don't want to crash, you may need to slow down.