Oil and energy has a strange property. The supply and demand curves are very inelastic in the short run (inelastic means supply or demand hardly change with price).
Think of it as, no matter what the price of oil, you still have to drive your car to work, or, if you were an oil man, no matter what price of oil, you still have to pump your oil well.
So a small change in demand or supply can bring about a big change in price.
In the long run, however, supply and demand are very elastic. For example you can replace a big truck with a small car, but that takes time, hence "long run".
So, a 5% drop in demand for oil can cause tanking of oil prices, indeed, it is not a small change in the context of short term oil price eqiulibrium.