However he made 3 passes over my house and i was using tree height for reference. In addition he was below tree- level when he dropped down over village. So definitely well below 500 ft...
How close to the tree were you standing?
To give you an example I live under the flight path to Southampton airport about 4NM out so when the planes pass over my house they are at about 1400ft, maybe a bit lower since my house is probably above the airport elevation.
There are a number of surrounding trees, several in the garden and some more in the surrounding fields, if I stand directly under the tallest tree and look up at a plane directly above then it is obviously higher than the tree that is about 40ft I would estimate. However about 200 metres towards the direction of the runway there are some more trees that are a similar height, if I stay in the same place and watch the plane descend away from me the plane very quickly gives the appearance of descending below the trees 200 metres away. Does it actually mean the aircraft is now lower than 40ft?
Of course not the aircraft is still almost 1000ft off the ground at the point were it looks to me like it has just descended below the trees.
My point is that unless you were standing very close to the tree and the aircraft was also no more than a few hundred metres away comparing to a fixed object is not a reliable way of discerning height above the ground.