It does look like it was printed using a 4-color process printing press.
But, rather than mixing colors using the CMYK blend, it may have been set up to print 4 SPOT colors -- Green / Red-Orange / Blue / Black.

The Black printing on the reverse did have poor registration, as easily seen.
Also, the ink mixes on the reverse may have been low and/or re-mixed & poor quality control, such as the darker green.

I would consider the chip shown as an error / variation, depending on your definition of the 2 terms. Definitely unusual.

These chip colors, spelling out "Nevada Club" did not always conform to the actual sign colors (6 different colors) as seen on the postcard below. (Postcard pic from MOGH / Chipguide.)