Thanks for posting the ruling ArabellaScott - it's an interesting one.
I wonder if IPSO might have been ok if the phrasing had been "a man who believes they are a woman".
(NB. I deliberately went for "they" here so as not to conflate two issues, as Dawson's complaint alleged misgendering and that goes to the part of the Forstater ruling that the judge left open to further testing, and I'm not talking about that bit here).
From the ruling, the issue is certainly around the disparaging nature of the word "claims", which has connotations of being a lie (which obviously GC would agree that it is), and it sounds like NobleWashedLinen's suggestion that IPSO are viewing this as akin to disparaging someone's genuinely held philosophical/religious belief is right on the money.
It feels like the distinction IPSO is trying to draw is between acknowledging that the person genuinely believes the gender identity thing themselves and suggesting that it's some sort of grift (which it obviously is sometimes, but there are also lots of people who genuinely believe they have a gender identity too).
It's especially interesting as the whole GRC thing is exactly that - someone claiming to feel like the opposite sex inside their own head, and needing a legal document to prove it as their inner feeling doesn't accord with biological reality.
But with actual religions, no-one needs a document to prove they believe their religion, as it's acknowledged that there is nothing to prove as you just hold an unfalsifiable believe (in god or whatever). And they don't need to 'claim' their religion is the correct one, as their beliefs don't require non-believers to participate in their religion for them to practise it.
I think the fact that IPSO have clearly referred to Forstater and are trying to follow that and the EA2010 to the letter is actually quite useful in furthering the debate, as it's clear they're treating it as an issue of how journalists should describe people with different philosophical beliefs aa opposed to stating that TW actually AW. As PPs have pointed out - IPSO didn't uphold the inaccuracy claim around Dawson being described as a man - just that using the word 'claims' was a belittling description of Dawson's gender identity.
So this supports the notion that gender identity is a belief rather than a fact, which lends weight to the argument that it should be handled in society like any other religion or philosophical belief and not as a scientific fact.