Left engine is critical on the 310 IIRC which would lead to a left yawing tendency in the event of an EF which is supported by the pics. Of course to have Vmc above stall speed then the operating engine would need to be developing high power....And the only logical reason for going full power on one engine during an approach is a go-around....Or low and slow and engine happened to fail at a very bad moment just as the power was being brought up and wasn't caught straight away. This would be odd though, you'd have thought that if you advance the throttles and you start to get massive yaw then you'd do something about it pretty sharpish (like close the throttles again and a boot-full of rudder).
Still if you fly the approach at blue line speed, which you should always (as a minimum) do in a twin then there should be sufficient safety margin to go full power on the good engine to go around.
Gear and flaps down plus a colder than ISA day may help reduce Vmc a bit too.
We can only guess at this one unfortunately. I guess though that they had an EF which the pilot didn't recognise quickly enough and at the same time encountered some situation which required more power, like a go-around or low-and-slow situation. Cheese, holes, lining up. Maybe he was just tired?!