It has been my experience that the term "terrorism" is usually defined according to a person's agenda rather than using any sort of concrete criteria, and is either expanded or limited according to such an agenda. Radical leftists defending Islamist terrorism like to expand the term by what they describe as "state terrorism", which includes any scenario in which people die. The hard right tends to exclude any action that does not fit the template of Islamic actions carried out for Jihad.
In the case of the church shootings, yes, it is terrorism because it fits the criteria for inclusion as defined. It is also a hate crime for the same reason.
As to those prattling on with their misunderstanding of the term "hate crime" and who lack the ability to distinguish between it and another crime, I would point out that a hate crime is committed against a random person because of what they represent, and not because of previous contact between the two parties involved or as a result of robbery or other criminal actions. As such, the act affects a much wider group of people because of the intimidating effects. A drug dealer killing another drug dealer over a turf war affects only those people and their associates. Killing people because of their race affects all people of that race.