A true cyan is a blue-green color, with a dominant wavelength (where you would point to on a color chart) of around 490nm.
This old style of cyan LED is known as "Tokyo Blue", as it was most often used in traffic signals in Japan, in the "go" part of the signal.
These days, most LEDs they call "cyan" have dominant wavelengths of 505-510nm, which is a distinctly greener shade of blue-green. Cyan LEDs are made more greenish on purpose to appeal to the most frequent user of such LEDs - United States traffic signal manufacturers. They appear green to the eye, yet emit enough blue to be visible to somebody with red-green color blindness.