what caused the price drop?

As mentioned earlier I also believe the overall result is positive.

Trading volume today is about four times the average trading volume. Have been trying to work out why sentiment changed today and the SP dropped. Maybe it isn't about sentiment.
Volume could be affected by those who recently bought this stock via margin lending. Most brokers have an LVR of 0(zero)% for NEA, so it is possibly one of the first stocks to go if some cash is required to avoid a margin call. Several heavyweights have gone ex dividend today (TLS, WES) and last week it was CBA. A drop in SP for those stocks could potentially trigger a margin call for some investors with margin lending.

There may be a number of reasons and differing views on the cause. I would be interested to hear of other views.

I don't expect to see this stock stay down at this level for very long. I topped up my holding today - fingers crossed.

IMHO it is a stock for the long term.

DYOR - I am not a licensed investment advisor.