They are claiming it was terrorism because that's their key to being exempted from liability. They had [some] anti-terrorism measures in place, and the law says if they did they are exempt from liability. So they need to have the case classified as terrorism, and so far the aw-thaw-rih-tays haven't chosen to do so. So they want a judge to do it for them.
I'm sure they have assessed the potential PR hit against the certain financial hit if thousands of people sue them, and made their decision based on the monetary bottom line projections.