It's a big planet and a small nuke. Although it would be a smoking gun, so to speak, either the sensors didn't find the fallout or the information is still classified.
As the article points out, pretty much every other bit of evidence points to a nuclear explosion.
No, it doesn't. In fact, almost no other piece of actual evidence points to a nuclear explosion with the exception of a disputed Australian sheep iodine measure that was unable to be replicated (including by New Zealand, who are nuclear-hostile and wouldn't assist in a cover-up).
In particular, there was no unusual seismic activity detected. There was no unusual hydro-acoustic activity. There was no fallout or radioactive debris detected. The New Zealand National Radiation Lab was unable to detect any radioactive anomalies despite being well within the fallout radius for a test in the area. Even the ratio of intensities of the two flashes differed from that in other recorded nuclear tests.