The article uses the word "partisan", the opposite of which I think is "independent", not "centrist" or "middle", but to be fair the article seems to conflate the two as well and never uses the word "independent". However to me there is a big difference between being a centrist and being independent. One could be independent with views that are at times deemed extreme right and at times extreme left. Similarly, some people are "centrist" yet somehow deeply partisan in the sense that their party can do no wrong and everything is the fault of the other party.
It is a valid question. I looked at the author's profile and while he is not from US ( Amsterdam ), his studies focus[1] appears to be on subjects that would suggest he should be relatively well acquainted with politics in US along with how they differ in terms of terminology from EU or UK. Sadly, I can't seem to say for sure how term was intended in the article itself. That said, the author does seem to reference individual US parties.
[1]https://www.uva.nl/en/profile/t/o/p.tornberg/k.p.tornberg.ht...
This. Partisanship is going along party lines (agreeing with the Party) where independence is thinking of your own free will. We desperately need more of those people in charge.
Insisting that truth is always in the middle is a radical ideology on itself.
The problem with this is that people are particularly bad at judging their own 'independence' of thought, regardless of their political views.
I would say the opposite of partisan would be someone who actively seeks to understand and relate to the views of those who they disagree with, or who are from their out-group. This would also imply independence of thought.