holy shit. the animal sanctuary was your exampleAdam Smith was not using the term self-interest in the way you want to use it.
Conflating self-interest, benevolence, happiness, and self-fulfillment is probably a sophistry that later 19th and 20th century philosophers engaged in.
Adam Smith was talking about self-interest in a tangible economic sense. He felt that while benevolence was admirable, in the real world most people are motivated by self-interest. And I don't think he was talking about working at the marine animal rescue sanctuary.
you missed out on the key word of rational
Me donating time to take care of dogs is both rational, and in my self interest because I can afford it and it makes me feel good. Just like paying money to watch a sporting event, or any number of other activities to occupy time in a capitalistic society