They are demanding a ransom, but Ransomware has a commonly accepted definition which requires encrypting files and demanding payment to decrypt them. [0]
They are not demanding ransom. Ransom is (per Merriam Webster): "a consideration paid or demanded for the release of someone or something from captivity".
They copied the data, and they want money otherwise they will release it. It's ordinary blackmail.
The very first sentence of that link would include this under "ransomware"
> Ransomware is a type of malware from cryptovirology that threatens to publish the victim's data or perpetually block access to it unless a ransom is paid.
They copied the data, and they want money otherwise they will release it. It's ordinary blackmail.