He's plugged in to that prop engine (not sure how it amplifies the signal or where the speakers are...)
I suspect it's just a tongue - in - cheek funny that seemed like a good idea at the time
The first thing I thought looking at that pic was "don't get yer cable caught in the prop... that would be bad...."
BTW...that,s yours truly plugged in to the lower cylinders of a Wright R3350 turbo compound radial engine, which,if and when it would start, would belch unbelievable amounts of oil..forever...The red axis sport is ......what can I say.....simply the best.....it really likes being plugged in to big amps, like this Wright 3350...