A more sensible (and piquant) explanation would be that the guy who measured the circumference had shorter arms than the guy who measured the diameter. I'm just waiting for a Biblical literalist to try to float that one. ;^)
Its not awkward. Its exactly what the verse says. It is you who are adding to its plain meaning and arriving at the conclusion that its awkward. The verse says the rim's diameter and it separately gives the measurment of the body of the vessel.
Your interpretation is awkward in that the author had to take two measurements of the same rim and no measurement of the body when one is all that is needed in geometry.
According to the text the author gives us
A. The width of the walls of the vessel.
B. The height of the vessel.
C. The total volume of the vessel.
D. The diameter of the rim.
The circumference of the body is the only missing variable.
So from this circumstance you conclude that the missing variable was not given and instead the author gave us a second measurement of the rim. You make this conclusion even though the given number would be within the range expected if it were describing the body of the vessel.
You partially justify your conclusion by making fun of the person measuring it even though the easiest and most exact measurement of the rim would be to measure its diameter and the only practical measurement to make of the body is to measure its circumference.
I respectively submit that after looking at the text in its entirety the conclusion that the author gives us two meaurements of the same part of the object is the most contrived conclusion.