Well it's a true statement. Not all oils are the same.
Take essential and fragrant oils for example, there are higher quality oils than others.
Using the picture above for reference, let me begin by saying if the oil sinks to the bottom as it does in pic.a it's not a high quality essential oil. Oils should float for a start so if it sinks chances are there is not much 'oil' in the product. Pic.a is actually a quality fragrant oil, and you will find most fragrant oils don't float and many are much more gluggy than the one pictured - typically these cheap oils are made to be used in oil burners. If you have an oil that sinks and is really gluggy/vicous it is NOT a high quality essential or fragrant oil.
Pic.b is olive oil. This is to give you an idea of how gluggy you don't want your essential oil to be. While olive oil, and many other natural oils, are good for moisturising the skin you don't want your essential oil to be so thick it doesn't absorb into the skin well.
Pic.c is a great quality essential oil. The oil floats on the top, it is not gluggy and it has that nice fine spread that works exceptionally well for absorbing into the skin.
Pic.d is also another high quality essential oil and has much the same properties as pic.c. When looking for a great quality essential oil look for oils that behave similarly to pic.d & c.
Hope that helps with choosing your fragrant or essential oils.