When a player hits the ball very hard at a top player, often the top player often effortlessly returns these shots as if he has reflexes far beyond those of normal people. This isn't really true. In fact, in non-table tennis things, where he hasn't trained for many years, he might have only average reflexes. And yet he seems to react instantly to these smashes and loop kills. How does he do this?
From years of training, a top player develops fast reactions to things they train for. You could argue they have faster reflexes in table tennis and be correct, but only for those things they have trained for.
But there's a second thing going on here. Most players barely react to an opponent's shot until the ball is coming toward them, or at most at the last second as the opponent hits the ball. But the reality is that the huge majority of the time you can judge where the ball is going and how fast almost the instant the opponent starts his forward swing. If you watch top players react to smashes and loop kills, watch how they begin to move into position as the opponent begins that forward swing – it's almost as if they know where the ball is going to be hit – because they do. (Not consciously, of course; it's all trained subconscious, i.e. muscle memory.)
How can you do this? It's all about observing the opponent, and learning to react to his movements. Just as you learn to subconsciously react to an opponent's spin based on his movements, you should learn to make the connection between an opponent's swing and the direction the ball will go, as well as its speed, spin, trajectory, etc., so that reacting to it becomes second-nature. You may have to observe this consciously at first, but soon it becomes a subconscious habit.
For example, you can read much about the direction an opponent is about go by watching his shoulders. So be aware of the opponent's shoulders, and you will develop the proper reactions to his shots, reacting faster and faster. It's not about having faster reflexes; it's about developing proper reactions that just make you appear to have fast reflexes.