Then they could call it one DC. A DC can have more than one building. But by saying you have several data centres you imply redundancy, similar to AZs at AWS. A

Then they could call it one DC. A DC can have more than one building. But by saying you have several data centres you imply redundancy, similar to AZs at AWS. And (at least to Amazon), two AZs are far enough away from each other so that one building could blow up without affecting the other one.