Like a lot of 'car' words that have different meanings in the US and UK (e.g. hood, which of course means the thing covering the engine at the front in the US but the thing you pull up in a convertible in the UK when it starts raining - or, more likely, the thing you drop down if/when it stops raining!) 'trailer' means something very different, although of course it's always something pulled behind the car.
The Americans call what we call a 'caravan' a trailer; what we in the UK call a trailer is pictured below (I'm not sure what the Americans call it?).
So that Vale is in fact towing a caravan not a trailer, just as it says in the caption!
