Is WhatsApp end-to-end encryption fake?

Since a while, some messages I receive are messages that are "Frequently shared". Surely, during the holiday season, I expect this to happen and it happens a lot.

However this raises a question. Whatsapp boasts having end-to-end encryption. How can Whatsapp determine that a particular message is shared frequently? One answer is that the hash of the message can be tracked. However, when a message is sent from A to B and then from B to C the hash will surely be different because A and B have different public keys, right?

In my mind, the only way that WhatsApp can assert whether a certain message is sent frequently is because

1. messages are decrypted in transit, or
2. messages with the same content have the same hash (meaning that there is only one key for all messages), or
3. messages are only partially encrypted

In all cases, there is no real point-to-point encryption. Now I am no cryptographer so I will probably have overlooked something. Could anyone please fill me in?