That depends on the details. Three to one odds are an immediate danger in my book if any of the three makes a threatening move.
From the article:
“The homeowner told police he saw a light in his garage Wednesday and found three people sitting inside a car.”
If he shot them sitting in a car, he is done.
Especially if the homeowner comes up on 3 people in the middle of a drug deal. There is fear of losing money, fear of going to jail, fear of being caught in an illegal act. All of these can mean that a lone man is vulnerable to attack from the three.
Even if one of them just gets out of the car, the lone man can interpret this as the beginning of an attack.
Exactly 3-1 means he was in danger. If they were that bold to be there, he had to assume they were a danger to him.