2 theories:
1. Team Clinton knew from internal polling that they were going to lose; thus, the reason for cancelling the NYC fireworks display, nearly a full week before the election.
2. Team Clinton/Clinton news networks/pubs were so shocked that Clinton was losing on election night that they ceased publishing/announcing the counts for about 2-1/2 hours. During that time, they were trying to find the votes to overcome. However, they began to realize that it would take upwards of 120% to 130% of votes in some major precincts. That would be a red flag for corruption. A few precincts did get away with having more votes than actual voters. Even that, however, was not enough to overcome the Trump lead.
Either theory seems viable. However, some reports were that some FED agency recommended cancelling the fireworks. Also, Clinton’s after-party [which she was too ‘unavailable’ to attend] was held in a room with a symbolic glass ceiling. So, theory #2 may be the more accurate one.
The fireworks were canceled Monday morning, 7 November.
The fireworks display was announced Thursday, 3 November.
I don't think either story came from the Clinton campaign.
When the original (Thursday) announcement came out, it was ascribed to a source in the FDNY, which issues permits for fireworks displays.
Original story about fireworks display permit was published Tuesday, 31 October 2016.
Here's a link to the Free Republic discussion of that story.
Here's the cancellation story, which was published Monday 7 November 2016.