Temporary Total Loss of Power

I wouldn't factor your oil PSI into what occurred due to it still being within range. Depending on your S/N range you are allowed to be @ 1.5bar when above 3500RPM.

I would focus more on the carb heat and electric fuel pump activation. When you turned on your carb heat, your engine went into a very rich running condition and when you turned on the E-pump at the same time, you may have exaggerated it even further if your floats are even slightly heavy (7.0g). It is not necessary to turn on the carb heat when you are on the final approach as you would on a conventional aircraft (Cont/Lycom). 

This was a major topic of discussion with flight schools who switched from Cessna's to the Rotax-powered Diamond aircraft and they were constantly pulling carb heat on the final approach as this would turn the carburetors and spark plugs jet black due to how rich the engine was running. There were occasions when the engine lost power when doing this. 

Check your floats to make sure they are within spec and try to avoid pulling carb heat unless it is necessary! 

It sounds like the event was farily binary, the power was there and then it was not but all the time it was running smoothly. To get that to occur without a fault you would have to somehow restrict the air flow evenly into both carbs.

My experience of carb icing is that you get a gradual reduction in rpm, it is not sudden.

If you get a fuel problem that only affects one carb then you definitely have a rough running engine.

It is hard to imagine an ignition fault that would result in a sudden rpm reduction where it was still running smoothly.

Is there anything inside the airbox that could temporarily block the airflow or anything in the engine bay that could block the air box inlet?

Kevin raised a good point regarding airflow blockage. We have seen flapper valves on some ALT air boxes fatigue and break off. The airbox flapper valve can fall into a position where it blocks airflow to the engine (depending on mounting position).

See photo's 

Blockage of the airflow is a good idea. It felt as if somebody has pulled the throttle backward. Exactly so. I'll forward that idea/question. Thanks!

If it WAS water: Would it cause that 0/1 - idle/full power behavior that Kevin called "binary"? Is this plausible?

I would have thought if moisture/water was inducted into the engine then this would result in a weaker mixture and rough running. The fault symptoms sound more like something impeded the airflow since this would have maintained a correct mixture and smooth running.

Is there anything missing in the engine bay? Something that could have come lose, partially blocked the air inlet and then fallen away?