Actually, that makes it more believable, not less. Let me explain why: A voltmeter can't just measure volts, it has to make a tiny current flow through a resistor. The value of that resistor will be lower for cheaper volt meters because the cheaper volt meters need more energy extracted from the circuit under test to function. A more expensive one has a very high internal resistance, and so loads the circuit under test far less.
In this case being able to supply 8 volts into a meter with a low internal resistance is actually a plus ;)
That said, the current is still tiny, even a crappy volt meter will pull no more than a few hundred micro-amps from the circuit that it is measuring. So let's be generous and say that it pulls a whopping 10 mA (very likely on the high side (edit: it turned out to be 37 uA)), in that case the power generated would be 0.08 W. Not enough to charge your phone by a long shot, but enough for a pretty demo with a moving needle.
Finally, these cheap meters tend to output complete nonsense values when presented with high frequency AC, one would expect that they would at a minimum measure power transfered using a dummy load and some kind of dedicated power meter.
All in all this does not make things look any better for uBeam. I'd really like to know who did their technical due diligence.
What's really bad to me - but I'm a nitpicker - is that in the video the lady refers to the volt meter as a power meter, which it definitely is not. It measures potential, not power, any power that it takes from the circuit can be chalked up to imperfect design and the laws of physics. Maybe the person doing the demo was not knowledgeable about the physics behind the equipment but that's betraying a complete mis-understanding of the basic concepts involved.
The transducers used appear to be of the piezo-electric type, those have a fairly high internal resistance and the voltages produced by those devices would be relatively high, the currents correspondingly tiny.
What gets me about this whole saga is that uBeam makes it seem as if they invented wireless power transfer using ultra-sonics, but any sound is wireless power transfer and that includes ultra-sound. The whole crux is how much power can be generated and whether or not there is a practical way to overcome all the obstacles.
To transfer some power doesn't prove a thing, when I whisper in your ear I'm transferring power using soundwaves...