The problem is with crosswind joins...IMHE...that many pilots think a "crosswind join" should be where the crosswind normally is (i.e. upwind of the numbers). I've flow with people who join like that and it makes my skin crawl as it is a recipe for disaster. Sticking OVER the upwind numbers gives greatest vis, clearance and least conflict. The only possible time there may be an issue is if someone goes around early and are back at circuit height by the end of the runway.
It baffles me why they didn't see each other though. The DA40 viz is pretty good.