Well, according to your logic, the Boston Marathon bombings (there were two bombs, I believe; hence, the plural) were not terrorist acts, unless they were intended to scare off runners from breaking a major sweat.
Causing the public to be fearful of participating in public events, is a tactic of terrorism.
The perp need not announce the reason for the act. Simply causing public panic and fear is a terrorist act by itself.
“Showing up at a large public event is a bad idea.”
This Oklahoma nut-job wasn’t going to convince folks that showing up at work anywhere was a bad idea.
It just didn’t have a cause and effect connection IMO.