That why you use multiple sources. The water polygons make it very clear, it’s in the water. Trees generally don’t grow in water (except mangrove forests but those are missing in the game).
FS2020 knows where railway lines are in general as it is in the TomTom road data that’s integrated with Bing maps. It also uses that data set to draw the road overlays. However the railway data in the TomTom (formerly TeleAtlas) database is only single line, not good enough to actually draw railway tracks, but definitely good enough to determine what could be a railway bridge.
The AI can determine the shape of buildings, it can determine the shape of the ship object. To determine how angular / rectangular a cluster of pixels is, is simple math. Add weights to all the info, it’s in water, it’s approaching a rectangular shape, it’s near a city (the data has town boundaries as well), more likely not to have trees on it.
It’s a work in progress, the game launched in beta version. A lot of things including Blackshark AI are not finished yet. But its far from impossible, not even all that hard a problem to solve imo.