Probably the worm was originally assumed to belong the Netsky family because of certain text in the messages it sends. A brief look at the code clearly shows that there is not much resemblance among both worms.
The following picture shows Netsky.AD (left) and Buchon (right). Needless to say there is no pattern to be seen.
As a demonstration of how variants among a family look, these are Mimail.A (left) and Mimail.B (right). The resemblance is quite apparent.
