Surface Water Overflow Not Covered

My insured has an endorsement for back up of sewer or drain water damage. The endorsement reads “The following additional coverage is added: We will pay for loss or damage to Covered Property solely caused by water that backs up from a sewer or drain. This coverage is included within the Covered Property Limits of Insurance. THIS IS NOT FLOOD INSURANCE. We will not pay for damage from water or other materials that back up from any sewer or drain when it is caused by any flood. Flood means the overflow of surface water, streams or other bodies of water, or their spray, all whether driven by wind or not.”

Insured has a basement office that has a sump pump to keep ground water out of the office. Recent heavy rains in northeast and a clogged water drain caused a pooling of water in a back courtyard/parking lot which then flowed under the back door of the office. An adjuster inspected and noted that the drain was clogged with debris and the water then flowed under the door. This is surface water, but it would not have pooled if not for the clogged drain. The drain was not inside but was in the parking area behind the building. Is this a covered loss?