You are correct. The idea was to show readings taken from a real-world object that one would wish to record detail in, using normal photographic metering techniques. All metering caveats apply. This was not a scientific test, nor is it relevant to anything else apart from that one particular situation. It's just an illustration of the kind of subject that Tim asked about, as far as I understand.
If you did only allow 2½ stops over the fully-illuminated incident reading for the brightest highlight, the actual brightness would be about 2½ stops over your allowance, in this instance.