Lovely to see @PyongyangKipperbang out of retirement, but sadly on this occasion, utterly on the wrong side of history!
While it is tempting to think that 'grass is grass', in most instances, caravan and camping sites allocate PITCHES. That is an area of grass, not a postage stamp the exact footprint of the caravan or tent you happen to have there. As the variety of posts on this thread has shown, many sites do explicitly state that the whole pitch is for the exclusive use of the owner/leaser/subletter/holidayer/overnighter, very occasionally, they don't.
However almost all sites, whether tents, caravans or (im)mobile homes have paths, 'roads' and required firebreaks. These are usually shown on a map which is given to every visitor on arrival.
Were you given a map like this (by the site or your friend), @Tevion28? Did it show a path to the river? (Usually a grey bit, arcing around long lines of pitches and accessing areas like riverbanks at convenient, if not necessarily the shortest, points.) If there's a map like this anywhere on site, you are CLEARLY in the wrong, I don't see how anyone could interpret that just tramping across a bit of group which is CLEARLY PART OF A WHOLE PITCH is ok, regardless of flowerpots, fences, or 'geroffmyland' signs.
Manners seem to be in short supply! (also by the lady who shouted, but she's probably fed up of visitors not taking their cue from maps and the fact that trailing through less than 2 metres from someone's window on a large, open, green site is clearly NOT the same as walking down an urban pavement in front of a row of terrace houses).
Hope you take your cue & find your open space manners for the rest of your holiday, you'll find everyone a friendlier bunch as a result, even when you make innocent mistakes!