George,
You could be correct with your assumptions on how much care is taken in the production process. However, I would suggest the the production process is exactly the same as it is for the "edible stuff", the difference being, the labelling.
If the product is going to Asia, Africa it will be labelled without the warning, and if it's going to the EU, USA and the like, it will be labelled with the warning!
To be honest, mustard oil is quite a disgusting ingredient without any of the health implications. I used to add it to my mint sauce, and thought it ok, until one day when I'd run out, and so made a batch without it. The mint sauce was much much better, and the mustard oil never got used again.
Ray
