This was not something I made up, but read specifically concerning changing oil in this engine. It surprised me too, but I believe the reasoning behind this tip is to assist in venting fumes from the crankcase, as new oil is being added. This prevents fumes coming off the hot engine from concentrating in the manifold and adversely affecting the PCV system.
The proper way to change any car's oil is to do it while it is hot. You get a complete drain of the oil and dirt has less of an opportunity to adhere to the sides of the engine. It also drains much faster.
Apparently, it improves ventilating fumes off the crankcase, as new oil is being added, and away from the PCV valve and intake manifold.
When I was 17 years old, and in engineering school, I thought the same way as you do. It wasn't until a number of years later that I found out that I was not doing right, for the reasons I mentioned above. You'll find out that almost everybody does it when it's hot for a reason.