I'm not sure it is a bombshell so much.
What it indicates is that China informally informed Japan, at a meeting, that they were considering it.
At that meeting a Japanese Defense Ministry official told the Chinese, "China has not announced this ADIZ to the international community, so it's impossible to say where our air defense zones overlap. As such, I cannot make any further comment."
So, what other communications occurred regarding it between that informal feeler and the "official," announcement?
Perhaps Japan felt there would be more talk, and in the absence of it, felt China had tabled it.
We just do not know.
But I do not consider this revelation as any kind of smoking gun. An informal feeler which the Japanese at the meeting indicated would be impossible to gauge their reaction to without more international input.
I have no doubts that the Japanese knew something was in the off'ing...I just think they felt there would be more pre-amble and reacted negatively when there wasn't.
As it is, IMHO, it is moot anyway because China has every right to establish an ADIZ for the purposes of monitoring air space approaches to their territory to identify potential dangers...and does not need Japan's, the US's, or the international community's approval to do so.
