Another suggestion was to set just the mood, word or colour. Somewhere on the forum there is suggestion to have a set of words that need to be used in a story…
I think you might be refering to my suggestion. Actually the words I mentioned were literary devices (tropes!) like metaphors, puns, irony, alliteration. Designed mostly as a way to make the story amusing and witty, as well as stimulate the writer towards a bit of humour.

Having volunteered to be a judge I suddenly find myself greatly in favour of a word limit! Though for me 5000 words is around 15 minutes reading time maximum, which isn't much really. I don't mind if they are a little longer than that.