Well it could be a fruit tree although I can say for sure that there have been no fruit on it during summer/autumn. I can't speak for the first 6 months of the year as we have only been in this house since July.
The netting?
Well who knows why that is there, it's some real flimsy garden edging soft wire type stuff. It's possible the previous owners put it up to keep the stay cats out but if that is the case it doesn't work.
Probably just to extend the wall height a bit as it is only about 4ft tall as it is.
Soon we will put a proper height extension of some kind up, more for privacy than anything else.