Wow!
I think it is difficult to know.
I think there is definitely a reason for thinking it could be airborne in terms of transmission. Particularly when people are singing, as that involves expelling a lot of air from the lungs.
One thing that came up in the South Korean case, was that people were very close together and repeated chanting "Amen!" (from what I remember), and this was speculated as one reason for the transmission (at least here on Japanese TV they said this).
But in the South Korean example, it was also pointed out that they held hands, and also ate together (Do you know if the choir practice involved going on anywhere else such as a restaurant or pub afterwards?).
But yeah, also it is very suggestive of a long incubation period. It certainly wouldn't surprise me.
Around the time of the Diamond Princess, the WHO were saying that incubation could be asymptomatic for up to two weeks, but also mentioned that some reports suggested an even longer period. Yet, because that two week figure seemed to be the most commonly cited, then the quarantine on the Diamond Princess (and those of countries repatriating their citizens from Wuhan and the Diamond Princess) was set at two weeks. I wonder if the number just stuck and became a default assumption without any further analysis.
As I said to lionking, we definitely cannnot presume that the life cycle of the virus itself is only two weeks. According to the Worldometer figures, there are still around 100 "active cases" from the Diamond Princess and 15 are still listed as serious or critical (as an aside, I don't know if this means they have been on a ventilator for around a month now, and if so, I imagine they must have a pretty grim prognosis - IANAD!).
Anyway, sorry, no answers, only questions from me.