It really was very nice of Bryan Talbot to visit us here; hope you enjoyed it, Mr. Talbot!
So, the central point he seems to be making is that THE NAKED ARTIST is "a book of intentionally silly anecdotes which I take many pains at pointing out aren't necessarily TRUE."
Not having read the book, I can't judge just how explicitly Talbot took those pains, but it's hard to argue with the premise when stated that baldly. Basically, none of it is true, so it's irrelevant whether it is well-researched, or takes both sides, or follows any journalistic or historical ethical guidelines. It's all in fun.
Apparently Dave Sim still doesn't see it that way, so I can't tell whether Sim has read the whole Talbot book or just the part about him, missing the "all in fun" caveats. So it's hard to tell whether Sim is offended based on a simple easily-corrected misunderstanding, or whether he is offended based on a more intractable Sim-ian misreading of reality itself.
Or maybe Talbot is misrepresenting his own book, and Sim is right to be offended? But what are the chances of that?