Not a powerlifting event again sorry no one here knows the actual history of the sport
It's not a powerlift Hankins, Powerlifting is Squat/Bench/Deadlift. Curl is a contested lift. Back up through about the early 60's, it was the most common 3rd lift of "Odd Lift" contests. Usually it was squat, bench, curl, but sometimes they threw in other stuff, depending on the promoter. I've seen old contest reports that had things like shoulder press or clean in there. 
But when Powerlifting was formalized by the early 60's, it went straight to Squat/Bench/Deadlift. The curl was sometimes still contested, as were things like say, the two man deadlift. But formally Powerlifting is the big 3.
Odd Lifts now are things like Neck lifts, Hip and Thigh, Steinborn squats, etc....