It seems weird to expect someone with no programming training (an IT guy) to either build or sign off on something they have no understanding of. In large/high stakes settings, being risk averse and knowing the limits of your understanding are very good traits.
Imho, this IT guy did his job, more or less. What was the testing plan for this AHK script? What edge cases were considered? Unit tests, integ tests.... was there a preprod environment for it? A trial run? Can you safely roll back if / when bad data shows up? What's the retry strategy for network or up/downstream fault tolerance? Is there alarm or monitor coverage for bad scenarios?
I'm not saying a bunch of people typing are error prone, if that's your take on my post. I just think that there's a VERY different set of risks (and therefore mitigations) between a distributed manual process and a large scale automated one.
The IT guy might have on some level recognized this and judged the possible loss to be way more than the "guaranteed loss" of the not-broken current process.
If I were an IT guy with low level skills, I'd be proud of myself for making that hard call.