In one sense you both are right. When a portfolio manager puts in a large block trade, its been common for a long time for execution management systems to optimally handle the execution, by breaking the trade into smaller pieces of varying size, at various prices over a period of time, to try to get the best execution possible. Proprietary systems have been built which are very good at that. So while the gross holdings of a fund might be set by a human, the executions likely are handled by software.