... the alerts go to Apple for human review. You think their human review won't notice a garbled nonsense picture triggering a false positive?
This should be read as "the alerts go to a barely-trained employee at a third party contractor like Cognizant[1] who has a quota of material to review every hour or they get fired and don't necessarily get points for accuracy for human review". I don't think Tim Cook is going to be double checking these images.
[1] https://www.theverge.com/2019/2/25/18229714/cognizant-facebo...