Soylent is classified as a nutritional supplement, which isn't the same as "food". It's the same umbrella things like body-building supplements enjoy being under, with far more relaxed requirements than "food".
Sources are well known, a quick search turns them up[1][2][3]. The testing procedure has been disclosed by Soylent during their last debacle, and there was discussion here on HN[3][4].
I used to buy Soylent myself, started at version 1.5 (powder in the bag). But come on, this sort of thing is seriously not OK. You need better quality control, and you need better (and more rapid) testing of product as it rolls off the line. Hunt and pecking clearly isn't getting it done, and problems are slipping out under their noses. It's people's health - nothing to joke at. "Move fast; make people sick" isn't a good mantra.
> FWIW, the ingredient in question is "generally recognized as safe" by the FDA
Soylent has no real idea if that ingredient was the culprit (and from the FDA's classification, it seems reasonable to suspect that ingredient is not the problem). For all anyone knows, it could be a combination of ingredients, or not an ingredient at all, but rather contamination in the manufacturing process.
[1] http://motherboard.vice.com/read/soylent-20-shipments-were-d...
[2] http://arstechnica.com/science/2016/10/reports-of-violent-vo...
[3] http://www.latimes.com/business/technology/la-fi-tn-soylent-...
[4] https://news.ycombinator.com/item?id=12812730
[5] https://www.youtube.com/watch?v=t8NCigh54jg&feature=youtu.be...