That's a dreadful response. They should have asked to have it back to be tested and you should have been given at least two fresh batches. One for the returned container and another for the trouble it's caused you.

I've never seen anything in castor even after some considerable time undisturbed although I don't use Sig. Castor can absorb moisture but only to about 2% and that looks like far more than 2% contamination. From the photos it looks more like dust or dirt to me which could only have happened at the factory if your container is still sealed. Castor left exposed to air over very long periods will oxidise (go gummy) but in a container like yours it would likely take decades. Normally the only thing that can happen with some castors is getting white flakes if the oil gets very cold which apparently only happens with castor that has chemically extracted oil blended with pressed oil.

Personally I wouldn't use that oil.