Jim Causley is brilliant

Jim Causley is rubbish

Jim Causley has a beautiful voice

Jim Causley can't sing for toffee

Jim Causley is the greatest singer of his generation

Jim Causley is a pretty good folk singer

Are we really to suppose that, were Mr Causley to read the above list, he would be alternately whooping with joy/bursting into tears based upon how convincing he found the truth-content of each individual statement in the series above?

Of course not.

S'OP didn't publicly diss Jim Causley. He publicly dissed Jim Causley's music. (And since when was dissing someone's music beyond the pale?)

I disagree that he did it in unmusicianly way; I'd say on a scale of 0-musicianly it was probably a 6.5.

I would agree that it could be construed as "unfriendly' - that's in the nature of disagreeable cricitism.

But friendship has nothing to do with it. That's why music critics generally don't review albums by their friends.