Hi @ErrolTheDragon that's how they get the trunks so large, yes. I'm not all that fond of the squat look myself, I prefer them to look like real trees. They are grown in the ground for many years, or collected from the wild under licence from the landowner. Quite a few are rescued from nature reserves where they want to get rid of tree cover and reintroduce a different habitat such as heath or chalk downland, many are saved from the clutches of developers who would otherwise bulldoze the whole lot.
There are so many myths and misconceptions around bonsai I hardly know where to start. It is definitely not a case of "chopping all its roots off and bending it into a funny shape" as someone once said to me.
You do find wild trees that have been growing in a rocky mountain crevice or similar, which have miniaturised themselves, Some of those are famous in their own right and can be well over a thousand years old. Nobody would dare attempt to dig them up.
Although originating in China, Japan and Korea, bonsai is now pretty much global. In the northern hemisphere and places like South Africa, the trend is now much more towards creating an image with a native specimen which then looks like a miniature of a tree in the wild. In the UK we are famililar with the Capability Brown landscape and many people train their trees in that image, so they look like a full-grown forest tree in miniature. In South Africa they recreate trees from the savannah, in the Med they use olive trees in the same way.
Unfortunately the first contact most people have with a so-called 'bonsai' is with the mass-produced s-shape imported ones you find in supermarkets and garden centres, and sold as indoor plants. Most of them are destined for the compost heap before long. Enthusiasts and hobbyists wouldn't touch those with a bargepole - they are intended to be sold to people who think that's what a 'bonsai' is supposed to look like.