Psychics do this all the time. They make some vague prediction that something ominous will happen in the future.
Then, sometime later when something concrete occurs (e.g., an earthquake, plane crash, or assassination), they say that's it, that's what I predicted!
It is certainly possible that some student of some ethnicity said something bad would happen to the U.S. in an argument.
Now after the fact, it is "remembered" that he was Pakistani, and he said the WTC would come down.
Call me a skeptic, but I would like to have more corroboration before I put any credence in stories like this.