What they are trying to tell you, even if they don't realise it or quite know the right language, is that the vehicles/people are a major distraction in the image. If what the viewer perceives as the subject of the image is not what you intended then as the artist you probably need to do some reworking or start over.

The objects that viewers see as the subject are leading the viewers' attention away from the thing you wanted them to be interested in. Usually things which have high contrast, colours and sharp edges are most likely to lead us and you can take steps to remove them or lessen their impact on the image. Humans are just tuned to automatically seek out recognisable shapes and see them when they may not even be present (in patterns of random noise, or clouds for example); so you need to remove or lessen their prominence in the image.

There may be some things you can do in-camera for example controlling depth of field to try to make foreground objects more diffuse. You could also look at different viewpoints (high/low positions), angles of view (both tilt and zoom) and your location. With landscapes/skies it's always worth having a polariser in the bag too, they can really make a big difference.

In post-processing you can adopt a reverse-cropping method, where you start with a crop at the absolute tightest fit to the most important item in the image and then expand the area to include areas of interest. Also in post-production you can look at using effects like blur, desaturation and adjusting curves/levels with a mask.

In the sample image the cars are in sharp focus, which immediately draws the eye and aesthetically they have no place being in the image at all. They stand between the viewer and the landscape behind when all you had to do was walk past them and shoot from there to give you the recession, or... for another view, go right up close to the puddle and get a really close-up of raindrops splashing, you're not losing any interest from the sky as it's overcast.

The cars would never make a good horizon or be useful as a point of focus unless they were the main subject. Their shape makes them naturally distracting, arguably they are designed to be seen to help prevent road accidents. They provide particularly contrasty bright and dark spots in the image which can only ever serve to be a distraction if your intent is to present some other aspect of the scene as the subject of interest.

Spend some time thinking about the different angles and distances available to you and how you might represent your subject at those distances. Have a play around and see what you come up with.