HA, I have no idea if that is an actual video or not, but that is what's known as a dud. A missile is classified as a dud when the booster arming signal has been sent, but the booster motor did not ignite. This can be VERY dangerous and lead to death or equipment being destroyed.
I'd rather have a dud than a restrained-fire. Restrained-fire happens when the booster ignites, but it fails to leave the launcher. It sits there cooking away, but stays stuck in the launcher. Much more dangerous & exciting.
Seems as if that launcher has some sort of jettison device which expells the missile from the shoulder held launcher if the booster doesn't arm. It could be a burst of high pressure air, or maybe a spring of sorts to jettison the missile. As long as the booster didn't arm, there's probably a built-in safety feature that ensures the warhead doesn't arm. At least I hope so.