What's incorrect about this? I guess you could quibble about what "quixotic" is supposed to communicate there, which is not completely clear to me. But he did leave, prominently, angrily. And he has forged new alliances with the right since then.
I mean we don't know his motivations but in retrospect he did immediately make a bunch of friends on the right, and align his work with their goals and messaging.
It's a judgement that you can disagree with but as a characterization it does fit the facts.
It seems pretty clear from my perspective that the Snowden papers were a high watermark of Greenwald's career. Everything else since then has been a cash-in on selling to the populist anti-establishment grift, regardless of fact. I wouldn't say Greenwald himself is "right-wing", but that end of the aisle is objectively more favorable to his beat.
It is truly sad that the right wing speaks truth to power these days. I mean when the Bushes, Cheneys, Roves, Boltons are feted by the left these days, one will have to skip past these traditional pigeon-holing.