This is a wonderful question. Unfortunately, the answer depends upon each individual reader and how well they come to understand what Poe is saying in the text, The Cask of Amontillado.
Some readers simply read for the fact that they are told to. Other readers may attempt to find the deeper meaning in a text, but fail to do so based upon their limited cognitive skills. Only active and engaged readers will be the ones who routinely find the underlying meaning in all of the texts which they read based upon certain skills they have mastered in reading.
As for the story, some may simply find it to be a simple tale of horror. Others, who analyze the text, will come to find that the story holds more than a simple horror story. The story does reveal a truth about people consumed by revenge.
For Montresor, his anger at Fortunato is a result of "the thousand injuries" against Montresor. While the reader never comes to find out what the "injuries" are, one can only assume two possibilities: that Fortunato really insulted Montresor badly or that Montresor is taking a mistake made against him a little too seriously.
Therefore, the story being a simple horror tale or a revealing of truth completely depends upon the reader and how much they see in the text. It is simply different for everyone.