What is the (most likely) technical reason behind temperature specifications?
The most common reason for electronic limits on freezing is the moisture absorption in molecule sizes large enough when frozen and expand cause microscopic wirebonds to shear.   (popcorn effect)

Although there is no problem with storage to -40°C, the rapid self-heating with microscopic amounts of frozen water vapour can cause the most damage.

Over the decades, plastic has improved in black encapsulated epoxy to improve the grade of moisture seals. 

But for clear plastic epoxy encapsulation or lens, the seal technology is not there yet.

I do not know which laser is used, but here is an example of such a specification.

You might be able to keep it running and go outside in sub-zero weather without the thermal shock of heating frozen H2O molecules in a well,
 sealed case, but operating when stored below 0°C can be a problem,  but not guaranteed to fail.