Your original argument, as I understand it, was that since Snowden made a claim in an interview that was not backed by evidence, and that claim was reported as news by others, current and future accusations against his personal credibility are not propaganda but legitimate rebuttals to those unsourced claims.

What I'm saying is I'm willing to grant that these offhand, unsourced statements, made in context of the man explaining his own motivations, should not be treated as anything more. Further, I'll grant that regardless of Snowden's personal credibility or lack thereof-- his credibility is unimportant. Further, I expect Snowden would agree with me, since he's said that he came forward so that this would not be about him, but about the questions we should be demanding answers to from our government. Questions to which Snowden himself is completely irrelevant.

It's because of that irrelevance that accusations leveled at his personal credibility, and thus at his personal statements, absolutely are propagandistic poisoning of the well aimed at discrediting his very real evidence.

Although in fairness, many of them may be mere journalistic incompetence.