It may just be they are called single mode due to the higher output and different wavelength used in long distance transmission.
You cannot mix SM with MM, they use different wavelengths, and while MM fiber is either 62µ or 50µ, SM is only 9µ across.
The name comes from the "modes" of light in the fiber. SM is very thin and uses long wavelengths, so there are no reflections in the fiber, so only 1 "mode". Multimode fiber is much fatter, uses shorter wavelengths, and allows reflections, which produce multiple "modes" and reduces maximum bandwidth because of the multiple arrival times.
Mac