Well, it's certainly suspicious that we never see anyone actually playing it, just some panning of still images that could have been edited to change the PSR-S670 model name to PSR-S675.
But it's not unlike Yamaha to bring different models out at different times. The PSR-S7xx and PSR-S9xx do tend to be announced and released together, since they even share the same manuals. But if I remember correctly the PSR-S670 was unveiled before the PSR-S770 and PSR-S970, which had us wondering when-- or if-- they would be coming out, and whether they would also have the Live Control knobs. So it would be "turn about is fair play" for the PSR-S675 to come out after the PSR-S775 and PSR-S975.
As for for whether it's real or fraud, there are far too many fraudulent videos being made, so we tend to disbelieve any video that claims to show a new model that Yamaha hasn't announced yet-- except every so often Yamaha does announce that model. That's why these types of videos are so frustrating-- one never knows whether or not to believe them.