I thought at first they meant parts of the viaduct obscuring the train,but having thought about it, the problem (for the screener anyway) appears to be the grass/weeds at the bottom of the picture.
Maybe a re-crop with less (or none) of them visible ? Anyone think this would help ?
I have to assume they're talking about the weeds/fence on the bridge itself. I've seen this rejection used for that before, but it varies screener to screener whether its an issue or not...