My hyphothesis after talking with chemists in the field is that someone reused a container tank for synthetic oil in order to carry rapeseed oil.
The rapeseed oil dissolves synthetic oil easily.
They probably thought nothing would happen because of ignorance on the part of the man that made it. He probably used water in order to clean the original tank.
We have some bottles today of the stuff that was retired from the market and could analyze it. There are traces on it of synthetic oil components.
This oil was sold in cheap rural markets, with a green colorant in order for it to look similar to olive oil.
Because of rapeseed accident, nobody in Spain uses rapeseed anymore. They use sunflower oil. Cheap oil from big multinationals that make things like cookies is basically Palm oil.
Palm oil is destroying a big part of the world natural environment.