Hi TD...
This picture has always shown to me a coupling I have known as a "Quik-Couple". Male/Female, a sliding sleeve to align and retain the two mates. The "Misaligned counter bore" I have assumed is NOT a machining fault, but the result of a loose connection where the male, the counter-bored part is vibrating in the walls of the recipient.
A "counter bore" is the attaching piece, "counter" meaning mate. Its "misalignment" responsible for the sloughing off of wall material.
The striae on the walls show a vibration that likely blew off the large pieces, and in so doing, opened up the "cone" of play that caused the brittle fracture you speak of ?