The passage is comparing two different theories and likely the question will ask you to draw a conclusion on the information. Dont get wrapped up in all the fancy words like tachyon. The real comparison is on theories not objects.

Here is what you need to know to answer whatever they ask you:

1. Relativity theory states no object can travel forward in time at a speed faster than the speed of light
2. Quantum mechanics states that a specific object travels faster than light.

Those two statements contradict one another. So in order to resolve the contradiction one of these two things have to be true assuming the relativity theory is correct:

1. Quantum theory is wrong because an object can not travel faster than the speed of light according to relativity OR
2. The specific object travels backwards in time(remember we are told that relativity only applies to going forward in time) and both theories are valid.

Understanding those concepts will give you a good chance at answering whatever the questions are.