No

A cyber attack is a cyber operation, whether offensive or defensive, that is reasonably expected to cause injury or death to persons or damage or destruction to objects.

Michael Schmitt et al; Tallinn Manual 1.0, pp 92
  • Cyber Operation?
  • Expected to cause death or injury to people or objects?
City of Atlanta Ransomware Incident does not match this definition. Here's a list of actual cyberattacks and and why this matters.

What happened?

Online services for the city of Atlanta were disrupted after a ransomware attack struck the city’s networks, demanding $55,000 worth of bitcoin in payment. The city would eventually spend approximately $2.6 million recovering from the attack.