IQ scores are derived from a lengthy testing process that requires the participant to complete a number of cognitive tasks.
Each task is scored and the set of scores is converted into an overall standardized IQ score.
There is no zero point for IQ.
They do not think of a person as having no intelligence.
Similarly for standardized scales of personality or other psychological attributes – a zero point is an arbitrary point on a scale and does not indicate the absence of a quality or characteristic.