A pipe bomb in a subway station is terrorisum. You don't have to have a rag tied around your head and smell like a camel to qualify as a terrorist.
I respectfully disagree. While this is certainly a crime, terrorism is more than a simple crime. Terrorism involves a political agenda with an aim to intimidate/cow/unnerve a society.
Until we know the who & why of this particular act, we can not conclude it was an act of terrorism.