A provisional conclusion that the pilot (RIP, Dave) was surprised by both engines failing is probably valid. With the extensive explanation of EC-135 fuel system features provided by some folks here, it seems that one would expect fuel starvation to hit one engine before the other: failure in serial, not on parallel.
If in this case that didn't happen, and both dropped off at the same time, the surprise factor / startle factor seems almost certain.
Lonewolf - that is one possibility, but I wouldn't rule out the possibility that the engines were intentionally shut down, but if so the reasons why remain a mystery.
BC