This device doesn't claim to "make" energy. There is energy all around us - it may be tapping into that somehow. As the report says, York Uni know what it is doing, however don't exactly know how.
Some Scientists, even if the thing works in front of them will disbelieve if they can't put numbers to it. Look at the ridicule of Eric Laithwaite by the established scientific community who carry the laws of physics around with them in their cases - he even invented the linear motor and Maglev train. He dared to say to them that something was happening in an experiment, outside the known laws of physics. Shock! Horror!!