This is not Leonard Nimoy disavowing Spock. It is just a catchy title of a memoir of how he became the character and how he had to occasionally separate himself from it and not look at the rest of mankind as “humans“ 😂
He highlights his tendency to get bored with the characters that he plays - this is the reason why he was happy that the Star Trek TV show ended after the 3rd year and why he left the Mission Impossible series after 2 years on it.