I would say that he's remembered as the writer of two of the most influential books opposing tyranny, rather than as an unwavering fighter against truth, clear thinking, intellectual honesty, and opposition to political lies and gangsterism.

Well, the article that started this discussion describes him in these terms. It is true that most people who have heard of him know him only as the writer of these two books. But among people who know more about him, as far as I've seen, he typically has this illustrious image.

Homage to Catalonia came out in 1938. 1984 came out in 1949. Is it possible that his experiences (perhaps including realizing what he'd been excusing) had something to do with 1984?

As far as I can tell, he never ceased admiring the "revolutionary" regime that ruled over Catalonia before the Communists took over. However, even regardless of that particular issue, his views have definitely never been particularly free of ideological bias -- and here I'm not comparing him with some unreachable ideal, but with other people who lived and wrote at the same time. Yes, he was certainly much better than the typical Stalinist intellectual of the time, but that's an awfully low bar to clear, and some other people managed to clear much higher ones.