They can get tall in gulleys around here. I cleaned up a fallen Blackbutt once, not much thicker than that, [it was growing on a creek bank and went over in a big storm] it was 150'/45m ground level to top.
Most councils around here have a similar rule to yours, the area I do most work is: within 5 meters it has to be less than 500mm @ 1m or you need to apply.
I'm not sure about Hornsby, I don't do much over there now but they have a good tree policy. No spikes except for total removal, is one.
Going by the bricks in that pic that tree was there long before the house, so I'd say they couldn't cut it down when building, so are now trying again.
It never ceaces to amaze me why people want to live in areas like that if they don't want trees, that little suburb, it's Berowra Heights is totally surrounded by National Parks.
