A few things before I answer the question:
This video is not a good example of how you should keep or handle your snakes.
Venomous snakes are unforgiving to keep. As much experience as you might have, a single moment of inattentiveness could kill you.
That said, let's go on with your question.
What gets people attention regarding the video is that the man is getting very close to the snakes, even touching them, walking amongst them, etc, and none of them are acting aggressively towards him, attempting to bite him, etc. Well, some of them (far from all) do raise their hoods and enter a defensive position, but he is totally ignoring that and grabbing after them, and they do not actually strike.
We should distinguish defensiveness and aggression here. A defensive snake stands its ground and looks to protect itself, and maybe its eggs. As long as you keep away, you're "ok". They might posture (hood up), throw a few swings to threaten a strike, but they'll mostly stay put. On the other hand, an aggressive snake will chase you, come at you and try to strike that way. Very very little species have a tendency to do that. Most snakes will stand their ground or try to actually get away from the threatening situation, instead of trying to retaliate. Most snakebites happen because someone is messing with an animal or accidentally stands on/close to them.
In the video, we see exclusively defensive posturing. The hooding, the few threatening swings, but no chasing at all. That in itself is not that surprising.
but he is totally ignoring that and grabbing after them, and they do not actually strike.
If you take a closer look at the first half of the video, you can see that in the bunch of snakes, there is only one animal that's actually defensive. Only one animal that is hooding up and threatening. The rest is either unaware of what he is doing or doesn't care, I don't know which. If you watch carefully, you can see that he actively avoids the one hooding snake and just grabs the rest. Those are too stunned/surprised by the grab and throw to immediately defend themselves. All the time he takes care to keep a (small, but) safe distance between his hand and the hooding snake. Probably just enough to stop the snake from striking defensively. If it wanted, it could easily reach out further than that, but that would be aggressive, so a difference in behavior.
Then, the defensive snake is brushed away with the broom, instead of being thrown.
The man also seems entirely unafraid of the snakes.
Either the man knows what he is doing and/or the man is completely stupid.
I am assuming that these snakes are defanged, or otherwise venomoids. I can not think of any other explanation for the situation observed in the video. However, I am not very knowledgeable about the topic, so I may be wrong.
Not necessarily, and as pointed out in the video, not likely.
First of all, defanged snakes don't have all of their teeth removed. Only the two venom-delivering fangs - for more about fangs, see here. This means that they would still be able to bite, but it wouldn't be able to inject any venom.
Additionally, I'm not sure why they would even keep and breed cobras in that quantity, but one possible application would be to milk their venom for research purposes (in other words, to sell for profit). Can't do that with their fangs removed.
Could it be that he has raised them from their infancy, and that they are sufficiently tame not to act aggressively/defensively towards him?
Given how they're thrown about, I doubt they harbor any warm feelings to him.
One more thing about defanging snakes. It's cruel. Venomous snakes need their venom, not only to kill, but also to digest. It has evolved from saliva and is pretty much needed to properly digest prey. It's role in digestion also explains why some species' venom have such destructive properties on tissue, but I digress. Defanged snakes have a significantly reduced lifespan because of this. At the same time I don't think these people care too much.
Did I mention handling snakes this way is stupid?
Another thing to note is that Cobras, with their hooding behaviour, prefer striking downwards to the ground. Comparing their defensive posture with a Rattlesnake for example, you can see that Rattlers posture in a fashion similar to a spring, where they can quickly stretch out in any direction. Cobras on the other hand stand tall and try to make themselves big, but as a result can only really move forward and downwards. That means that if you stay high enough, you are "relatively safe".
