In multistage devices detonation of the primary with a failure to ignite the secondary is also considered a fizzle.
Fizzle is a generic term generally describing a failure to meet design yield. That failure can occurr for any number of reasons.
Brad
If it was 5-7kT, I'd bet it was a real fizzle, not a Castle Koon type fissile fizzle like you describe. In fact, I actually had to search to find an example of a secondary failure that someone called a fissile. As I never encountered that usage in my experience.
Basically, 5-7kT is an interesting yield as it means it's either a really good weapon, or a really shitty one, but since it's the norks, I'm going to say it's a shitty one. If shitty one, that yield is a true fissile, whether or not it's also secondary failure (if it was intended to be a multistage, then it wouldn't count as a secondary failure, as the primary is the fissile). If it's a good one...well, then it's also not a secondary failure, as the primary should have done better or it was a full yield good small one.
So at that yield there really isn't a way to describe it as a fissile because the secondary, if present, failed.
It was either a regular old fissile, or a really good little test that worked correctly.
Any further comment...well, I can't go there.