I was thinking about this as well, who knows...however what we are told is, the test was in the air. It might be coincidence, unless there were acknowledged sub-oceanic testing - are there "signatures" for such testing that exist??
Like the undersea volcano eruption near Tonga was it several weeks ago, last week - these may also be natural temperature-regulation mechanisms of the earth to cool things back down. Pretty harsh but pretty real.
If it is from underwater testing, its either: there is some nation or group doing underwater testing and the korean air test was a cover, or, its conducted by u.s., european or other '1st' world nations, as has been done for decades already and continuing, especially those who haven't ratified the test ban treaty.
http://www.rense.com/general61/earthqua ... misand.htm [may or may not have seen, not the original source - but rense seems to comes up for me, as one of the first in searches but thats unrelated].