I can't remember how much of this is implied canon or my own interpretation, but I fully believed that Chiron recognized Percy was a son of Poseidon from the fountain incident with Nancy Bobofit, knew that a child of the Big Three being claimed would be a total shit show, and simply chose not to say a word about it
wait isn't it also implied somewhere that Sally was in contact with Chiron at some point before Percy arrived at CHB? Im dying imagining a convo between them about Percy's godly parentage like-
Chiron: Unfortunately, its fairly common for the gods to not disclose of their godly nature, so a lot of parents don't exactly know who-
Sally: Oh I always knew Percy's father was a god! You see I met him at a beach in Montauk and-
Chiron: You know what Sally š I'm going to have to stop you right there.
Chiron after going to Yancy at Grover's desperate request and getting one (1) look at the child that is the carbon copy of Poseidon's preferred mortal form:




















