The above ground ones usually have more round/smooth traits and are near water so that helps a little.

This is a concretion that started forming soon after the shale/mudstone, in which it was found, was deposited. They are almost always roundish/bulbous since minerals precipitate in the pore spaces of the sediments surrounding whatever(in this instance, the fossil) initiated the formation of the concretion.

That concretion was probably recovered from the rock within arms reach of where he cracked it. If you notice, there are little shards of broken shale fragments in the gif where this guy was quarrying the rock.

source: geologist paleo guy that has cracked a shit-ton of them.