I don't see the problem. The ATCO asked for fuel remaining, and thought he heard "54 hundred", which clearly could not be the case, and was missing the denominator. So the question was "How many pounds of fuel remaining did you say you had? If you'd rather say endurance, that's cool too", it wasn't "Could you convert that to pounds for me?" When the answer comes back in KG, he takes it and deals with it. It sounded pretty well handled on all sides.
And Mr. Atienza got the transcription wrong. It's clearly "did" with the tongue on the top of the palate between the ds: Did declare. There's no nasalizing there.
Now that LX out of Pulkovo, that's some quality Engleesh for you.