Infared Night Vision works by using a infared flash/spotlight, lighting up an area in infared light and then using a special scope to be able to see everything it lights up. This is a really outdated method and has been used since Late-WW2 by the germans. Basically GEN 0 Night vision, but a system that a lot of older cold war era vehicles use.
Thermal Infared is a scope that actually picks up the difference of temperatures between things, and renders an image in accordance, without actually projecting anything(AFAIK). This is what FLIR is.