Well, that's not what some Americans think. I guess a sweet note mysteriously hidden away in a vault for 63 years isn't as fun as something else more interesting.
People will take anything and turn it into a conspiracy lol. She wrote the letter in 1986 to be placed in the time capsule in Sydney. It's been sitting there for 36 years already. It likely does not have any earth shattering revelations. It's good click bait for the tabloids though.