Miguel started the GNOME project (with, obviously, lots of similar involvement from other people). He is closer to a manager, ie, a person making the decisions. He can just say that the proposed article is nonsense and that is pretty significant evidence.
> he is also still a human being, and thus is subject to bias, deception, forgetfulness, mis-remembering, etc.
Microsoft threatening legal action is not the sort of thing that slips the mind.
> That's why if you want a real discussion it's useful to have evidence
The evidence is Miguel says it is nonsense. You can spill a lot of ink and not come up with anything half as convincing. Miguel's one line is more evidence of why GNOME acted as they did than the entire article managed to scrape together, unless Mr Liam on Linux happens to also be on the GNOME core dev team and I've just never heard of him. But I don't think he was. I doubt he was in the room or involved in any of the decisions.
Besides the fact that he did not give a reason why GNOME/GNOME 3/Unity happened, he is also still a human being, and thus is subject to bias, deception, forgetfulness, mis-remembering, etc. That's why if you want a real discussion it's useful to have evidence, not just whatever hypothesis sounds good to an in-group.