No, that's not why you so often see reference to the defined safe level of toxins in water when talking about foods. FDA does not always have standards defined for levels of those toxins in food, but there might be a level defined by EPA for water. If you want an official, scientifically plausible number to fall back on, the level defined for water is at least something.
For example, FDA didn't have a defined safe level of arsenic in rice-based foods for infants until 2020, and there's still no defined safe level of for adults AFAIK. There's nothing mysterious about this: the ag industry lobbies against these standards, and lobbies to weaken them as much as possible when they exist. But babies are cute, so eventually FDA made a standard, at least for infants - after years of pressure from groups like Consumer Reports.
The paper referenced in the article says:
The U.S. Food and Drug Administration (FDA) has proposed an action level of 10 μg/L of inorganic arsenic in apple juice (USFDA, 2013).
which suggests that at the time of writing, there's isn't an official number defined by the FDA. Based on the language on the FDA's website [0] I assume "draft guidance" (which has been in existence as a "draft" for a decade) means producers won't be held accountable for exceeding the numbers there.
https://www.fda.gov/food/environmental-contaminants-food/ars...