Nobody can count the machines. Hashrate is inferred: given the difficulty, the observed block interval implies a rate of hashing, quoted in exahashes per second. Daily estimates smooth the luck of block discovery; short windows are noisy.
The mining desk publishes complete-UTC-day estimates and compares equal windows rather than quoting a single day's figure, and it says plainly that this is not a measurement of installed hardware.
More observed work per second does not identify its location, owner or cause.