The concept of indirect fitness must be more complicated than explained here. The article explains it as a worker bee sharing 75% of her genes with her sisters, but only 50% with a child, so there is selection pressure for workers to be sterile and self-sacrificing. But few genes actually differ between individuals, so the percentages are much higher. E.g., I share ~ 99% of my genes with each one of you reading this.…
Could worker bees be fertile and have a selfish traits that let them have more children, they would only have a 50% chance of passing these, because children share 50% of genes.
So: 75% of altruistic genes pass vs 50% of selfish genes. Altruistic genes win. Humans can't pass 75% of their genome this way, so that altruistic genes have no intrinsic advantage over selfish genes.