This effect could be achieved with a "standard" superhydrophobic coating (or superhydrophilic for oil-based condiments). Those can be easily done with something like a nanostructured silica film (without having to functionalize the coating with additional chemicals), and silica is a very common food additive (fumed silica is already added to ketchup in fact to alter its flow properties)
The problem is that even benign materials can have unexpected outcomes that depend on their nano-structural properties. Carbon is safe, but carbon nanotubes can form cysts [1] and cause brain damage in fish [2].
You're absolutely right -- there are some materials that would be very bad candidates here.
I was pointing out only that this can be achieved with structure only (no additional hydrophobic/hydrophilic chemicals), and that it can be done with materials that have already proven themselves inert when ingested in nano-scale particle sizes.
