I'm callin' BS. I maintained infrared sensors systems in the USAF (remember the spiffy nighttime bombing videos from Desert Storm?) so I've logged quite a number of hours watchin' this kind of video.
An IR system that would record a puff of gas at normal body temperature as being opaque would be useless. If fart gas looks black on screen, what would the air on a hot summer day look like?
But there's an even bigger clue that the fart is fake. They guy's arm, which is presumably warm, is white...indicating the system is in a white=hot mode. Therefore, black=cold. When was the last time you tooted off an ice-cold fart? Me personally, I've never gotten a frosty feelin' in my shorts from lettin' one rip. :glassesgr