First of all, it's not actually a flamethrower.  This is his device:

 

 

This is a real but low end flamethrower:

 

See the difference?

What he has is called a "weed burner."  They're sold in literally every hardware store in the country and have been for at least 50 years.  They cost about $30 unless you put a fancy shell over them. They require a propane tank.

Literally almost every farm, and every landowner with an acre or more, owns one to control brush and weeds.

Congratulations, urban liberals! You've discovered "Fire"!

And just as with every discovery, you want the government to save you from your own imagined stupidity.

Sample comments from various articles:

"It's just a matter of time before someone walks into their office, torches it, drops this thing on the ground and runs! Then what?"

So...just like anyone could do with a can of gasoline, or a jar of gasoline and a wick? (A "wick" is a flammable textile used to bring flame to a fuel for purposes of ignition.)

"They need to ban these before someone sets California on fire!"

California gets set on fire all the time.  Also, CA already has a law that requires permission from the fire marshal for any kind of burning. it's almost as if fire existed before you discovered it last week!

"It's bonkers that these aren't considered a firearm!"

Not really. A firearm discharges a projectile by means of an explosive propellant in a fixed cartridge.  This does not use explosive, a fixed cartridge, nor fire a projectile. Therefore, it is not a firearm. You don't just randomly get to declare things "firearms" because they scare you.  

Also, fire projecting technology seems to be about 3000 years old. https://en.wikipedia.org/wiki/Early_thermal_weapons It's good to see you're finally getting up to speed on technology.

My advice is to smoke some medical marijuana to calm your nerves, be careful of the lighter you use to do so in case you set your house on fire, and let the adults handle this.

Also, my preferred source is www.FlamethrowerPlans.com for plans, parts, kits and complete units at prices very competitive with Musk's, with much better output--up to 50 feet.