Ah, so it's more the fact they said that they were talking to the ground crew rather than the fact they were?
No. The two should be synonymous, if the Nigel has any cred.
what's your definition of a 'mandatory frequency'?
I don't feel any urge to make such a definition, but I'm quite sure that listening to Ground when manoeuvring on the ground would fit it. Aren't you?