With high-heat accelerants, burns can compromise or destroy the skin in gruesome ways, opening the way to horrific infections that can easily kill you.
This summary, "sending the officer to the hospital with burn injuries," doesn't tell us whether he's still there. It doesn't say whether his trip was to get a quick lookover to make sure it was nothing serious--kinda doubtful, considering the charge)--or deep scarring, organ damage, etc., or similar danger to life.
"Makeshift flamethrower," to me, doesn't say "harmless prank that went a bit too far." But I guess we'll hear.
The guy’s bail is one million so the judge failed to catch the humor.