The ruling occurred because Panera Bread Co. was trying to prevent the White City Shopping Center in Shrewsbury from leasing space to Qdoba Mexican Grill. Panera Bread's lease agreement stated that White City Shopping Center would not lease space to any other sandwich shop.
The legal ruling stated that "A sandwich is not commonly understood to include burritos, tacos and quesadillas, which are typically made with a single tortilla and stuffed with a choice filling of meat, rice, and beans."
Expert witness Chris Schlesinger stated in an affidavit that "I know of no chef or culinary historian who would call a burrito a sandwich. Indeed, the notion would be absurd to any credible chef or culinary historian."
UPDATE (November 13, 2006): The commenters at Jamie Zawinski's blog take the discussion much further.