The scale is different. Setting something on fire is a localised event, typically dealt with by local and/or state authorities. Taking out parts of the grid (re

The scale is different. Setting something on fire is a localised event, typically dealt with by local and/or state authorities. Taking out parts of the grid (remembering that grids are interconnected) is a state and potentially inter-state affair, and it is reasonable for state and/or national authorities to get involved. As another commenter noted, such investigations are not mutually exclusive. They can (and should) both happen.