The text presented was one continuous piece of prose. I gave a brief run-down on how picture book texts were presented, and we tried to see how the text would work within spreads rather than pages etc. It became clear that a lot of the text did not translate into images and that the action was static ie located in one place without forward movement. In other words, the text was not working as a picture book text - which is not to say that it wasn't working as a piece of writing or a story, just that it didn't fit the market that the writer was aiming at.
This seems to me to be a matter of fact, not opinion. Publishing is full of facts like this. If a short story comp states a maximum of 2000 words, then 2500 is too long. Full stop. The writer can choose to cut 500 words, or send their story to a different competition, that's up to them, but the parameters are clear. If someone is looking for apples, they don't want pears, no matter how beautiful the pears are.
I don't think it's being unkind to present these facts. If anything, I think it's unkind to pretend that these facts don't exist. Sadly, I believe the writer misunderstood 'the text does not fit in with the technical requirements of the format you're aiming for' and heard it as 'this text is no good' and was hurt. For that I am sorry. But it still doesn't stop the facts being the facts.