Coolant does not need to be drained, however you never know what a tech might do to make the repair faster/easier. The bulletin does call out that the transmission cooler has to be flushed and flow checked. This might be what the tech told the service adviser but the adviser may misunderstood. Filling the electronics cooling system takes about 5 minutes, the drive motor battery cooling system takes about 30 minutes to fill properly. A 20 mile test drive should be enough to check the cooling systems and to make sure the bearing repair fixed the issue. If there is another problem, they may not be telling you until the figure it out.