That's bad rules reading - it's an IT car, with an IT cage. IT cars may run in ST. The car is legal.

counter example: if you wanted to run in Production, and ran a non compliant cage, then the tech would be correct to point out that your car did not meet minimum production safety requirements as the PCS does not state that IT cars may compete in IT trim. The fact that some IT cars meet production requirements does not mean that they must or that those which do not may run as production as-is.

the STCS specifically states that IT cars compliant to IT rules may run in ST.

If this is really a problem, write a letter to the ITAC and request that the cage rules in the GCR be referenced within the ITCS, then a car prepped to IT regs is specifically compliant in ST with a cage that does not meet ST rules.