The inventor had the hypothesis before he had the device, so it isn't a True Scottman drift. He hypothesized, he wrote about it, he formed a company to own it (that being how science works now). A few brave people tested it, and it seems to work. Each successive test excludes the factors that could have invalidated the previous tests, and now NASA has a group on it. And, it seems to produce a thrust. Okay, interesting.
We'll all be sad, should it come to nothing, but at this point the inventor has a hypothesis to cover the effect, described a machine to produce the effect, and now we have machines that seem to produce the effect. I've read his hypothesis, and damn, I don't have that kind of math or science and never will. But, you know, if he described an angel-making machine, and someone built the machine and made an angel, at some point you have to look at the damned angel flapping away in front of you.