a) last ping not on the hr
b) initiated by aircraft
c) probably due to RAT (for a very short period) powering up after both engines stopped
That's what you need to explain
Pontius if A,B or C wrong please correct
Once the second engine failed (together with its generator), due to fuel starvation, the only fuel left may well have been in the APU feed line from main tank to the APU in the tail.
The on-board logic within the electrical system, with both generators off line, is automatic APU start so we may well have seen the "aircraft initiated ping" when the APU generator came online, all be it briefly before it also ran out of fuel.
The power from the RAT most certainly would not have powered the satellite system.