BOAC:
I firmly believe we may never know what happened. Two things will be known already - track and estimated speed at impact from the wreckage trail. There is a good possibility that altitude (but not height and track) could be established over the flight. Without reliable witnesses as to position and heading at any time, the rest will be conjecture
We know with certainty that he was too low for that location. What we don't know is whether the contractor was in compliance with whatever structure lighting requirements your aviation authority mandates.
Lighting of "temporary structures" in the U.S. is all over the map, no pun intended. If a building is being constructed in Manhattan where the crane would be lower than surrounding buildings the lighting requirement would likely be less than if the building was higher than the surrounding buildings. But, in the FAA at least, these decisions are left to indifferent clerks.
The contractor, if he was really smart, would have required strobes, if that is possible during the day when the crane is in operation. Then again, if the crane can be lowered when not in operation, that would also seem to be a prudent action.