It's probably not just oil, but rather a general reduction of risk from investors. People are worried about the global economic climate and are pulling their money out of stocks and putting it into more predictable, dependable assets like gold and treasury bonds, which tend to have much lower yields but also much less risk of tanking in value during bad times.

I'm not an economist, but my understanding is that the price of oil does not directly impact the valuation of these companies, per se, but that growth-oriented companies (especially) and oil sales depend on a strong global economy.

When the price of oil falls, that indicates that people are pulling back on oil/gas/etc purchases due to constrained budgets, reduced business/operations, etc. (and/or that people buying the oil predict that others will cut back on those things in the near future)

IMO nothing is unrelated when it comes to the markets. A fall in a primary sector of the economy will lead to uncertainty in every other sector.