No, it’s not a flamethrower. This was captured from a low resolution video, and shows the intense muzzle flash coming from a short barrel AK firing Russian 7.62 x 39 mm ammunition. The duration of this fireball is so short (on the order of a few milliseconds) that the video camera rarely caught it at all, but it can be easily seen in low light by the human eye. The muzzle break redirects some of the exiting gasses, making the fireball even larger. It’s hard to be sure, but it appears that the bolt carrier has not yet begun its rearward stroke at this moment. The AK is an AMD-65 with UltiMAK M7-B mount and an Aimpoint CompC3 reflex sight.