If this were a Muslim who slammed his plane into a government building because he was angry about our policies in the Mideast, I don't even think that would qualify as terrorism. Terrorism has a purpose of using fear and violence of achieve some political objective.
I think that very few people in the public sphere would share your definition IF this guy's name had been Abu Snuffy and he'd left a rant about Israel or Afghanistan on a Facebook page somewhere.

Given what we know, I'd put this guy, Abdulhakim Mohammad, MAJ Hasan, Richard Poplawski, and the Holocaust museum shooter in the same general category. All had major grievances that were based in political/religious ideology, but all also appear to have had significant personal dysfunctions. None appear to have acted as part of an organized group or had a realistic hope that their actions would achieve any kind of political objective, BUT their targets were clearly chosen for political/religious reasons.

I think choice of target + some political/religious motivation = a terrorist act. A different sort of terrorist than, say, KSM, but one nonetheless.