OZ,
The pilot was lower than 4,000' when the engine failed and he was not over Otago Bay either.
His first option turned out to be a non-goer due to vehicles parked around the particular sports ground and by then the only viable option was the highway.
Google Earth does not give a good indication of the terrain around there where there are precious few sites for a forced landing. North was not an option.
The engine did not immediately quit but initially lost some power. The pilot used that time to gain another 300' where it quit completely but he still only had about 2 minutes glide time available. Not much time really.
There are several people being quoted by the media expressing opinions on what happened. They are just that, opinions. No one at this stage knows why the engine quit and the wreckage is currently sealed by the Police.