Regardless of cause, that's a collision. If there was nothing they could have done to prevent that incident, if any reasonable driver would have had exactly th

Regardless of cause, that's a collision. If there was nothing they could have done to prevent that incident, if any reasonable driver would have had exactly the same problem, then perhaps they're not at fault. If somehow other people managed to navigate that hazard without issue then there may be an element of fault. Were they driving too fast? Were they slow to react? A good lawyer would be able to argue that the root cause of that collision was the spill on the road, which seems like a reasonable defence. If it went to trial a jury would be inclined to agree, so there's no real risk of over-prosecuting here. Keep in mind that these sorts of cases are the exception, not the norm.