That comment was based on Allen's account of Ballmer and Gates plotting to dilute him – a dick move by any measure, esp. after Allen showed his good faith on a number of occasions.

Gates and Allen were friends at when they went to school together. I went to the same school some years after them, and drew my own opinions based on first and second hand experiences with both of them.

No matter what you believe about the quality of their friendship, there's a teaching lesson for co-founders in their story.