There are all kinds of maybe boring reasons why this effect might, it could be that just talking about people is enough to get them to think about donating more than one sticker. It could be that the animal story made them put them in a better mood and in a better Mood you just don't care to share. Who knows? There are a lot of interesting questions that you might ask about why this is the case. And it's not clear that this is the best test of actual morality to give a kid you never saw one of your stickers.