Hi, that diagram shows you how the manufacturer set the IC up to measure the quiescent current that is quoted in the specs for a 0 and then for 1 on the inputs.
This current is the current supplied by the Vdd.
This sort of spec is only relevant if your are using hundreds of them in a circuit, even then its probably insignificant.
Or if you had only micro-amps of supply current to use.
Do not over think this, in most / 99.999% of cases this is insignificant.
By the way you answered your own question in your first post, the I in the circle represents a meter.
Tom...
