It's most likely that the drone that crashed was similar in size to the type of bird that was spooked (Mavic Mini to Mavic Pro range; maybe a Phantom at most). Anyone flying a larger drone (Inspire and up) would have a serious license and familiarity with permits, therefore unlikely to be called "illegal".
I'm guessing it either fell after colliding with a bird or was flying low enough with sensors off and clipped the ground.
Thunderstorms have been happening with some predictability since before birds even evolved. A buzzing, hovering, and erratically moving clanking mechanical thing is extremely novel.
Which of those two would the birds have a genetically and socially built-in way to cope and survive through?
Thunderstorms are likely rare in this location. Most of coastal California only experiences such storms less than once a year, depending on when they begin nesting any rain at all may not be common, as typically they is little rain from April to October.
