The 5 dimensions refer to the precise control of 5 degrees of freedom of nanogratings. 3 degrees of position in spatial coordinates and two degrees of polarization aspects. It’s in the paper and not phony, although the word “dimension” might be better replaced with some other word that doesn’t sound like 5 spatial dimensions - which is not what is intended. Before saying something is phony you should probably read the paper(s). That is from one of the top optoelectronics experts in the world.