They're confused with data set (2,3,5)
I believe the answer is:
at the ready
'set' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'they're confused with data' is the wordplay.
'confused with' is an anagram indicator.
'theyre' with its letters anagrammed with 'data' makes 'AT THE READY'.
Can you help me to learn more?
(Other definitions for at the ready that I've seen before include "Prepared for instant action" , "Poised for action" , "on standby" , "Prepared or available for immediate use" , "dipping hand in till?" .)