since John Brune is now dead,and cannot confirm this unless we hold hands and have a seance, I am making an assumption.
I am assuming his reason for fooling MacColl, was to expose the nonsense of categorising singers, he did this successfully, he fooled none other than Ewan MacColl[fact].
I am not sitting in judgement on any one or defending anyone, merely trying to undertsand why Brune impersonated a traveller singer.
it clearly wasnt to make life more difficult for traveller singers or to sabotage the radio ballads, otherwise he would not have owned up.
your statement about impersonating and funny voices, is a deliberate attempt to muddy the waters, the Kipper family and the others you mentioned were not trying to show, The ridiculous categorisation between revival and traditional singers, if MacColl was fooled it proves one thing, that unless the collector knows the category beforehand there is no difference musically.
another example of this was Bob Blake who would never have been collected if the collector[mike yates] had known he was not a traditional singer.its time this phoney categorisation was exposed for what it is BUNKUM,this categorisation is about as useful musically as those middle class victorian butterfly collectors