Has Antarctica's coastline been completely mapped? (map discrepancies)
The key sentence here is

(not sure where the dataset is from)

Every cartographer has to decide what level of detail to use. Mathematicians discovered the Coastline paradox for themselves in the 1960's, but it has always been a fundamental part of cartography.
Different sources of data will come out of different methods of data collection, digitization, and storage.
Regardless of the method used, somewhere there has to be a cutoff. You can't represent a detail smaller than the pen you (or computers) draw it with. The cutoff may be a concsious decision of the cartographer based on the purpose of the map, or an effect of the software used. Or just carelessness.
But this means that different datasets and choices of representation will result in a radically different appearance of the map.