YUY2_3840x2160 is already compressed with a lossy compression compared to rgb. Each 1x2 rgb block is represented by 8 bits of gray, then 8 bits of one kind of color information, then 8 bits of gray, and then 8 bits of a different kind of color information. You need one gray and the two color components to create one rgb pixel, so each pair of pixels shares the color information but has independent brightness.
The lossy compression is not spatial, but rather the loss of independent colour information between pairs of pixels.
The matlab drivers create rgb pixels as best possible from the YUY2 components. The matlab drivers do not compress the resulting image.