Oh dear, Jack, that is not very charitable! You asked for info, and it has been provided.
I have no reason to doubt Sheena’s word. I have written tunes myself, and having heard many thousands, it is not unlikely that odd “soundalike” phrases may creep in, and Sheena has acknowledged that possibility with her own tune in what she has said there.
As for Matt McGinn, he did detail any known tunes used for his songs, as you’ll know if you have a copy of “Matt McGinn of the Carlton” or “Scottish Songs of Today”.