They are demanding a ransom, but Ransomware has a commonly accepted definition which requires encrypting files and demanding payment to decrypt them. [0]
They copied the data, and they want money otherwise they will release it. It's ordinary blackmail.
> 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.
(added emphasis)
Here's the third sentence from that very same paragraph:
>It encrypts the victim's files, making them inaccessible, and demands a ransom payment to decrypt them.
Not everything can be explained in a single sentence.