Even at 25m, with a 37L53, they were lucky to get a 'catastrophic kill' on a Pz VIE.
Pz V, Pz VIE, Pz VIB were all very sturdily made, had good ammo/fuel storage (from a safety standpoint), and good fire extinguishing systems.
Get a copy of the book 'Panzer Battles of the Waffen-SS'. It's basically a large # of platoon and company AARs from Waffen-SS Panzer units.
The number of times those AFVs 'caught fire' in the engine compartment...crew bailed out...and reentered vehicle to continue fighting once the extinguishers had done their job - it was a surpisingly common occurance (and goes a long way to explaining 'claimed destruction of enemy MBT' by Allied ground attack types - smoke from the MBT, crew bails out...must be a kill - totally reasonable assumption if you think about it).
The main cause of 'catastrophic kills' vs. AFV was fuel fire detonating ammunition. The bigger and faster the round the better chance of this in general, and some MBTs (pre-'44 Shermans are a glaring example) had very poorly protected fuel and ammunition, causing them to catch fire and (eventually)/or explode even vs. 'non-extreme' penetrations.
It sounds like they hit that Pz VIE from so close that the penetrating rounds had enough power left to actually start a fuel fire. I don't think the MA ammunition exploded though - that would have taken the turret off most likely (88mm charges are pretty 'explosive').
Mike/wulfie
p.s. 'catastrophic kill' = total destruction of AFV and all crew.