Most likely, it was a terrorist act (i.e. designed to create terror in a certain group of people as part of a political or religious statement). But since it was likely done by Christians or some other good ole 'murcian boy, it will just be called arson or possible something generic such as a hate crime. We've had a number of terrorist incidents in the US over our history, but unless it is done by a group that we currently don't like, it never gets called as such.
If you aren't clear on this subject, here are just a few recent specific well known examples:
- Planned Parenthood clinic shooting (3 killed, 9 injured) in November of last year (Christian)
- Multiple black churches burned last summer (white supremacist)
- Sikh temple shooting in 2012 (white supremacist)
- Shooting at a BLM rally in Minneapolis (5 injured) in November of last year (white supremacist)
There have been dozens of other terrorist acts against planned parenthood, the black community, and non-Christians over the past decade alone.
Here is a listing (scroll down...note that there are 4 pages worth) of those types of activities in this century (2000 thru 2015). Notice that there are a lot of them. The biggest difference in the US is that most groups aren't will to admit their association with the attack, whereas groups like ISIS take pride in admitting to terrorist attacks...even if they weren't really involved. Heck, even in that database, you will find a group called "Veterans United for Non-Religious Memorials" which doesn't even exist (the confessed vandal used that name in a letter, but there is no evidence that any such group actually exists).
http://www.start.umd.edu/gtd/search/...#results-table