These practices include such offenses as fertilizing garlic with human feces and forms of sewage, growing garlic in sewage

From https://www.mcgill.ca/oss/article/you-asked/it-true-garlic-china-grown-human-feces-and-watered-urine

there is no evidence that garlic in China is fertilized in this fashion. In any case, there is no problem with this, human waste is as effective a fertilizer as is animal waste. Spreading human sewage on fields that grow crops doesn't sound appealing, but it is safer than you might think.

That would be my guess too at first glance. What do they think manure is if they're grossed out at sewage? As long as it's treated properly to reduce pathogens then it's just "ew yucky I don't like the real world".