IR sight and Thermal Vision sight are one and the same thing, you are complicating a very simple idea, they are both IR apparatus, the difference between one and the other is one is active the other one is passive, active requires the outsorce of IR light, the passive uses a cooling chamber for imaging (and there is another way to view objects at night, in a passive way, by amplifying ambient light sources)
if you want to get technical about the terms your explenation is sufficient but like I said it just complicates a very easy idea, passive/active

so which one is mounted on the MG in the picture?