Ball joint fell off!!!!

[doubledoyle]

Hi guys i need some advice,
Last saturday whilst out driving one of my lower ball joints came un done dropping the truck down onto the front suspension. I can't understand how this happened, only 3 weeks earlier all the ball joints were checked and had new split pins.

Ive only had the truck on the road 3 weeks and the previous owner had disc brake conversion and a new master cylinder fitted.
Am i right in thinking that i could have ball joints with the wrong taper?
seems like maybe if the ball joint was locked then everytime i turned it may of been un doing the nut on the bal joint?