Floyd Landis admits he doped. The admission is news. It's not really news that he doped. I think pretty much everybody knew that already.
Do I believe much of anything Floyd Landis says? Not really. It wasn't believable when he had a new story every five minutes for why his test results were positive even though he supposedly wasn't doping. When he stepped up to the microphone, darted his eyes around and said "I'll say, 'no.' " to the question of whether he doped, he looked entirely like a man who made a conscious decision to lie to the entire world. When he drunk-dialed another cycling athlete to harass him for urging Landis to admit the obvious, he went from reprehensible to pathetic.
So Landis' claim that he knows Lance Armstrong doped has as much credibility as most of what has come out of Landis' mouth the last four years: almost none. The evidence is that Armstrong didn't dope. New evidence could change that conclusion. But Landis' claims are not credible evidence about Armstrong's doping. All they are is credible evidence that Landis is still more interested in running and hiding than he is in facing up to the fact that his whole adult life is a lie.