Yep, fake.
Unless the guy was farting liquid nitrogen for some reason.
The IR video was calibrated to be "wite=hot, black=cold". It can be flipped to black=hot, white=cold, when that enhances contrast, since the electromagnetic values of IR radiation are arbitray to normal human eyesight anyway.
I don't doubt that under FLIR, that flatulence wouldn't show up, or at least leave a "stain" of warmth in the offenders pants, though.