That doesn't mean the technology can't be improved, and there's actual science being done. Brains are being imaged. There are peer reviewed articles published every year that details the challenges of how to model brain damages. It's not fair to brush them off as just an invention in marketing.
So far it does seem that measuring impacts at an angle matches real world brain damages better than the older standards of measuring dead-on impacts. That's what "rotational acceleration" means. Acceleration is just another word for impact. It doesn't mean your skull should rotate freely.
There are enough indications that this translates to helmet improvements that most consumer organizations have started to recommend them should you buy a new one. That doesn't mean you should throw away your old helmet but it should be enough to disqualify it as "snake oil".
This new Wavecel system hasn't been reproduced yet, two testing institutes has so far failed, but it is similar enough to existing cell and slip systems that performance is not likely to be worse.