Why TTN call the user payload a "MAC Payload"?

Hi all,
The MAC Payload is defined by the LoRaWAN specification and consists of a frame header (FHDR) followed by an optional port field (FPort) and an optional frame payload (FRMPayload). The Frame Payload (FRMPayload) is the “user payload”. TTN documentation is in accordance with the spec [ https://www.thethingsnetwork.org/docs/lorawan/message-types/#:~:text=MAC%20payload%20of%20the%20data%20messages ]
In TTNv3, in the End Device Live data, I can’t understand why TTN says MAC Payload for the “user payload” whereas it should be written Frame Payload.
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I first taught of a mistake, but as it has never been corrected, I’m now wondering if the MAC Payload in TTN has another meaning.
Thanks.