The way i handled this is to actually use square tilemaps that overlap and are offset to hex positions on odd even y index.
There is a skeleton example below that could be extended to do the above although that topic focused on performance. The basic structure lends itself to this topic.
What you see in the image is most likely overlapping hex map with multiple layers were the top layer is mostly transparent with edges that are not. Most likely the selected tile is based on hex sides that connect and the tile used is automatically selected.