The issue is you did not credit him initially. Are you saying that he was credited in the initial publication of the article and his screenshots that show this is not the case are fabricated?
It doesn't just make a huge difference - it's a different thing entirely. Credit where credit is due, initially and up front, is being honest. Changing it after and pretending like it was like that the whole time is trying to cover up your own actions - that's arguably even worse than the initial plagarism. (At best it shows the same underhanded streak as the plagarism itself.)
Completely despicable. Added TNW to my hosts file.
The screen shots don't go all the way down to where the current version online has him credited twice. So it is hard to say if they were already there or if all three credits were added at the same time after being called out.