What do the numbers mean on a three-position switch?
The most likely conclusion is:


The dotted line indicates that internally the two switches are mechanically linked. meaning that they switch over at roughly the same position and instant.
Each switch has three possible settings:


NVG: 2-3 and 5-4
ON: 2-1 and 5-6
OFF: 2-none and 5-none (in the photo this is the top position)



Since nothing is connected to 4, the 5-4 connection is not needed, but the designer probaby chose an off-the-shelf product.

Technically, you would call this a double-pole, triple-throw, top-off switch