Although the two words sound similar their implications are very different.
Think of an allergic reaction. It’s not something we have a choice in. Our immune system is triggered by an outside influence and it goes into an automated process to protect us from the threat. In the same way when we react to something that happens in life it’s usually not a choice but an automated process. Our past experiences that have shaped our personality, especially the negative and traumatic ones, lead us to see the perceived threat through the eyes of our past experiences and we react, automatically, as if we were back in the past. This often leads us to behave in ways that are inappropriately suited to the situation at hand or cause us to overreact to something that may not have been a threat at all.
By contrast a response is more conscious. An accurate perception of the current events allows us to behave in a way appropriate to the situation and get the best possible outcome, since we are seeing clearly in the present moment and not reacting from past experiences. This is not to say that the past does not matter, ideally we learn from the past and use it to educate ourselves in how better to deal with the present. The difference here is that when we respond we see what is actually happening, rather than what we think might be happening.