I enjoy a good conspiracy theory as much as the next guy, but if it's true here the people are idiots. Insurance payout is the same whether it happens in the middle of the day or the middle of the night. I'd want to make sure nobody is around to see it fall, or maybe one or two people just close enough to be credible when they say they didn't see anyone near the building to knock it over.
Doing it with a couple of little old ladies walking by and a firetruck coming up the street? I don't think so. Getting caught in insurance fraud is bad enough - why risk manslaughter/murder charges when you intentionally drop the building and it lands on somebody?
Accidents happen on construction sites; people get lazy; things break in old buildings. I think this was just an accident - an accident caused by negligence, maybe; a happy accident for the developers, quite possibly - but still an accident.