Well, there's a few things going on here that allow them to claim 170mpg. This is not yet a car, it's just a design exercise. As far as I can tell, they haven't yet expressed an intention to build a prototype or a mule.
They claim a 48% engine efficiency, instead of the Prius' 37%. The engine is just large enough to maintain 60mph @ 6% grade. The biggest advantage of a hybrid is that you're able to carry around just enough gasoline engine to do the job. Unfortunately, the Prius dropped the ball on this one with its 1.8L engine. The Ingocar will have an advantage here, but I wouldn't count on 48% efficiency until they build a prototype.
"An air drag of 0.22 is used in the calculation of fuel consumption." That's achievable, and Toyota could have done the same with the Prius. They chose to settle for 0.25, for various reasons including aesthetics, convention, and usability.
"a weight of 2,200 lb has been used in the calculation" which seems extremely optimistic to me. I think 2800lbs is more like it for a modern car. Accordingly, they'd need to up-size the engine.
Here's a pdf with a few more technical details than the website:
http://www.valentintechnologies.com/...-Car-05-07.pdf