"The botched launch triggered false alarms in South Korea and Japan. Cell phones in Seoul blared out warnings to prepare to seek shelter, while alerts in Japan advised residents on the island of Okinawa to take cover. Both were later canceled when it became clear that the projectile posed no threat."
"South Korea's military released pictures of what appear to be pieces of the rocket, which it salvaged from sea, possibly allowing the South to analyze the North's rocket technology."
These quotes from the article would suggest that the more trustworthy sources of Japan and South Korea feel confident that it did in fact fail. Apparently the second stage of the rocket which was supposed to take the satellite much higher into the atmosphere failed. That isn't the type of thing that you can easily hide.