Wow, what a letter. I don’t recall NASA ever sending such a letter to nearby residents.
Are they concerned the 180 meter “hop” may get a little out of control?
My thought would be more from a likelihood of an explosion at the pad or nearby. With that much LOX and LNG in such close proximity, if the rocket exploded or crashed into the fuel farm tanks, it would make one heck of a bang. Enough of a blast to shatter windows for miles and miles, I’m guessing?