How is it not E2EE? Are you going by a stricter definition than commonly used?

> End-to-end encryption (E2EE) is a system of communication where only the communicating users can read the messages. [..] End-to-end encryption is intended to prevent data being read or secretly modified, other than by the true sender and recipient(s). The messages are encrypted by the sender but the third party does not have a means to decrypt them, and stores them encrypted. The recipients retrieve the encrypted data and decrypt it themselves.

Which requirement do you believe is failed by such a system?

It is incorrect to refer to encrypted backups as e2ee. See the wikipedia article on the subject [0], at the bottom of the "Modern usage" section.

[0] https://en.wikipedia.org/wiki/End-to-end_encryption

> Some encrypted backup and file sharing services provide client-side encryption. The encryption they offer is here not referred to as end-to-end encryption, because the services are not meant for sharing messages between users[further explanation needed]. However, the term "end-to-end encryption" is sometimes incorrectly used to describe client-side encryption.[23]

This is reasonable, but it's not describing any weakness of encrypted backups. It merely points out that "E2E" isn't the right term to use when there are not two E[nds], but rather only one client and their files.

However, our conversation was about storing chat history. There are two parties to the conversation in that case.

The key property of E2E is that only those parties can read those messages, and nobody else, in particular not the agents running the server. That property is not affected by the existence of backups, as long as those backups are client-side encrypted, because third parties cannot access them.

Therefore, it is possible to have both cloud-stored chat histories and true E2EE. QED.

The wording there has no effect on security, it's semantics. E2EE being an application of client-side encryption for messaging.