How could you tell the difference from that photo? I am not questioning that you are right but rather how you tell the difference from a Rough-scale snake.
Basically I can tell @ a glance because of all the keelbacks I rescued as a kid on the sunshine coast in S.E.Queensland. In that area there is both keelbacks which mainly occur in the lower coastal areas and the rough-scales which I have also encountered often while spending time looking at everything that moves in the higher mainly rainforest areas in the mountains behind Brisbane (Mt. Glorious and Mt. Nebo). Anyway, I've never really given a great deal of thought to how it is I distinguish between the two but now that I have, the rough-scaled snake has a more distinct head, less streamlined to the body when compared to the head of the keelback. Aftyer a while you develop an eye for it and can pick it at a glance. I am still absolutely sure its a keelback.
flip the body upside down, if the scales after the vent (subcaudals) are undivided (single row) then its a roughy, two rows its a keelback. Also look for fangs. Chances are its a keel back.
When I lived in that area I would not play with keelbacks, and regarded them as dangerous, far to simular to roughies and I couldn't tell the difference without flipping it.