Domestic pigs are Sus Scrofa subspecies domestica, and are genetically little different from wild boar (sus scrofa). In the same way that the domestic dogs are a subspecies of the grey wolf. So when domestic pigs escape in an environment which contains wild sus scrofa, of course they interbreed.

I have certainly eaten wild boar meat in France which was at least billed as not being farmed. Wild boar sausages and burgers in the UK, there I am less sure. Is the meat more tasty than, say, Gloucester Old Spot? There I am also not sure, even having eaten both.

Of course Australia, New Zealand and North America have no indigenous populations of Sus Scrofa. So all wild boar there are descended either from escaped domestic pigs, or from ones escaped from zoos, or in some parts of North America from deliberately introduced ones (why would anyone do that??)

Dave Hanson, are you sure there is not a selection effect there? The farmed boar which would have grown larger didn't do so because they have already been killed and eaten?

As for Hylochoerus (Giant Forest Hog), according to Wikipedia they have never been domesticated even in Africa. I have never eaten one of those.