Not to sound cocky .. I'm seeing plain as day a GLARING ISSUE
On the Fractured tube at threaded end there is a machined area inboard of threads that the Female spigot area of connections O-Ring rests on when fully screwed together. This places the actual sealing ahead of threads, leaving threads in Shear and not radially exposed to pressure .. as it should be.
Tho picture shows NOT ONLY a Sheared away or damage O-ring groove at the end of the female spigot, BUT AN O-RING at shoulder of where tube butts up when fully screwed on ... WTF !!! Ed's shared drawing shows NO SUCH O-RING at that position
With the O-ring omitted due to perhaps a previous Fupaw of o-rings groove on end of the spigot, one was placed where tube butts up ? .... This alone places pressure Radially on the threads and would create such a failure IMO.