The German expert is using the “ignorance as proof” argument – “you cannot prove that aliens didn´t do this, therefore they did do it”. He lacks any corroborating evidence to “obtain independent confirmation of the facts” the aliens seemed to fail to provide any further evidence of their existence other than flipping one bit in Voyager´s computer memory.
The mystery is why did Voyager go wrong in the first place. NASA Scientists took a different approach to our German expert and focussed on fixing the problem. They discovered that simply flipping a single bit of Voyager´s computer systems (the space-probe equivalent of turning it off and on again) caused Voyager to begin working normally again. This implied some kind corruption in the computer memory on the probe – the kind of corruption that can afflict electronic device when subjected to electro-magnetic interference. Research has now shown (partly thanks to Voyager´s efforts) that Jupiter actually has an extremely powerful magnetic field which is also the exact type of interference to cause corruption to Voyager´s systems. This is the basis of NASA´s “alternative hypothesis”. This also seems a more simple option, obeying “Occam´s razor” of the more simple explanation. NASA certainly acted on this hypothesis providing the Juno probe (mentioned in “Jupiter has liquid metallic hydrogen ocean”) with extensive magnetic shielding.