It's worse than childish. The people called out in that bizarre tweet would probably have a conversation with their staff or the police about whether they or their families are in any kind of danger from this apparently popular guy wishing death upon them from the internet, or perhaps from one of his idiot followers.
They might not know much about where Tan is coming from, but they know they work in a building where Moscone and Milk were assassinated.
They would be perfectly reasonable to hire private security and sue Tan for damages to pay for that and whatever other measures that seem prudent for their own protection along with the pain and suffering that goes along with the very reasonable fear this tweet and its effects caused.
What he wrote was more or less the limit to what you can say before it becomes a serious crime.
They might not know much about where Tan is coming from, but they know they work in a building where Moscone and Milk were assassinated.