What part of pilot recording the audio don't you understand...Im sure the crew of the Beech recording their flight just happened to catch the transmission..I've heard this many times, wishing I could record it, cool that he did, it's just a taste of the random stuff you hear on your adventures through the skies.
As PIC, in short, you can delcare an emergency for any given reason if it deems unsafe for operation. Being any kind of aircraft planning a landing overweight, there is most certain an emergency onboard and touchdown over MLW (max landing weight) creates stress outside the norms of operations, creating even more of a situation. Not all aircraft are capable of dumping fuel.
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Ryan