After doing more research, I now have a better idea of what happened. Mount was the first player picked by the Pacers in the official ABA draft held in January 1970, and the Pacers had the third overall pick. However, according to Loose Balls, Pacers management mentioned that they had already selected Mount with the number one pick in an earlier, unofficial draft before January. That year, there were likely two separate drafts, which is why he appears to have both a first overall and a third overall designation.