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I'd assume it's an XLSX simply because that's the format they received it in from the Defense Department.

Looking further at the metadata, the author is "Williams, John A DLA CIV DISPOSITION SERVICES" and the company is "Defense Logistics Agency"

Yes, the file is 1033-program-foia-may-2014.xlsx - just the fact that 'FOIA' is in there suggests that it's the original format.