The display of the 38 mm watch (38 mm refers to the height of the whole watch body, including bezel – it’s ill-fitted for calculating pixel density) is 21.22 mm wide (0.8354 inches) and has 272 horizontal pixels. That’s 325.6 ppi.

The display of the 42 mm watch is 24.34 mm wide (0.9583 inches) and has 312 horizontal pixels. That’s also 325.6 ppi.

That’s the same pixel density as the iPhone (excluding the 6+ with a higher pixel density and older non-retina iPhones).

Now you can argue about whether typical viewing distances for watches are closer or farther than for phones (whether or not a screen is “Retina” is always a function of the typical viewing distance and the pixel density, never pixel density alone and there is no single device independent pixel density that is “Retina”), though I actually think on balance they are probably slightly farther or the same.