I wouldn't call it a weasel word because it describes accurately the fact nobody gave them the authorization to use the likeness of Attenborough, and there are laws to protect people's likeness in multiple jurisdictions (https://en.wikipedia.org/wiki/Personality_rights) that might require such authorization (whether they could be applied in the case of AI remains to be tested, but apparently most of them do not question the "means" to impersonate but the act of it).

It raises an interesting discussion about this though, how is this different from someone making an impression of him and doing a comedy show of it for example. They also had to listen to him for hours to reproduce the voice correctly, are they now infringing some copyright when they use this voice?

To me, as long as you clearly state that this is an impersonation/parody, and there is no deception, I do not really see a reason to protect this, even for music. But I'd like to hear arguments for a protection and how it would be enforced, how do you judge of the likeness, how do you know/prove which source material was used for training for example.