Bad luck, but least they came down from the $1,035 fine a bit.
I agree they had too much of a knee jerk reaction to banning all drones from the N.P. system, especially in areas where no one was around like your circumstances. Accidents happen as to why the few that led to the ban, but there are probably many more who have dropped a camera into a lake or some thermal geyser area off a boardwalk and they haven't gone overboard by banning all cameras too - although I have gotten into issues where if you have "pro looking gear" they want a commercial film permit which can cost maybe twice your fine.
Curious did they make you take down the video too? I saw the BLM permit thing on the Red Rock Canyon post where the BLM "Wants a copy of a 'permitted' flight" which I thought odd. Maybe they use it to tell if some Youtube video was a permitted one with the copy, and any not permitted they'll go after? Dunno, but any fine is getting excessive and a way to make money. Friend's kid sped up to blow through a red light camera and they got him for the speed and red light with a fine of $1,250 with all the sundry added county court fees added on as well.