And not all muslims are terrorist. and what do you call the Hardcore Gamers in this country? they're terrorist too, and they're not muslim.
https://www.youtube.com/watch?v=YnOF7y-KuHE This video addresses the whole "not all Muslims are terrorists" statement.
And "Terrorism" isn't actually a very well defined term (there's a ton of debate over what is and is not actually classified as terrorism, definitions change from country to country etc). From the definition I like to go by: mass shootings are not acts of terrorism because they are not made because of ideological reasons, they are made by mentally unstable individuals.
For example: A terrorist would crash a plane into a skyscraper because he hates the ideology of the country in which said skyscraper is located. A mentally deranged person would shoot up a theatre full of people without a real reason other than just being mentally ill.