Someone doesn't keep up with domestic terrorism.
Covenant Sword, and Arm of the Lord, KKK, Animal Liberation Front, Alpha 66, Aryan Nation, Army of God, Black Liberation Army, Earth Liberation Front, The Order, the Jewish Defense League. Nevermind the Timothy McVeighs, Terry Nichols, Eric Rudolphs, Theodore Kaczynskis, and Robert Dears.

If you believe that 99% of terrorists are Muslim, you're just not bothering to look (or ignoring) plenty of domestic actors that aren't Muslim. Don't be fooled, every religion, race, and creed has their violent extremists.