The thing people have got to remember is that gregson missed all of december and part of january with his stress fracture. He has obviously worked hard on the cross training and has since got some good sessions done but this does not substitute for consistent training over a good period of time.
i think he has the basic level of fitness to run a great 1500, which he did in 3.37. but the 5k is a different beast and i think it showed last night he just didn't quite have the strength. i doubt whether he is anywhere near as fit now as when he ran 29.06 10k in terrible conditions beating all of australias best distance runners 5 months ago.
The kid will only get better and if he gets over to europe later this year you'll see more improvement i guarantee it.