In article , lid
says...

Or would it have been grown in such a small pot, but then i find it amazing
that such a big tree would have grown in one successfully?

See bottom RH picture he
http://www.bigplantnursery.co.uk/olives.html

and an interesting bit of that link which says

"The mature olive trees are often harvested from old olive tree groves
which are being removed to make way for more profitable varieties, as
global warming continues to affect southern and central Europe."

Janet.