I agree. But not like a Stuka. And not at a rate which might tear the aircraft apart - that cure would be worse than the disease.

If you look at the numbers on Flightaware, you will see that the aircraft left 41,000 feet at about 1050 "BST" (I'm never fully confident of Flightaware's time zones). It reached 7,000 feet at about 1105, 15 minutes later. That's 34,000 feet in 15 minutes or about 2,200 fpm on average - which is much more plausible. During the descent, the highest vertical speed figure given by Flightaware is 3,900 fpm, and >3,000 fpm was only sustained for about 5 minutes.

Now, in the light of the hysterical numbers you were given, how reliable is the rest of your source's information? Is it even confirmed that there was a fire on board, as opposed to merely smoke (from some other reports)?