Looking at the author’s Reddit post apparently things like exclaves were intentionally omitted for simplicity’s sake.

https://www.reddit.com/r/MapPorn/comments/gxwn5r/oc_the_topo...

Still doesn’t explain some things, like, why is Singapore (an island) shown on the map as having a border with Malaysia? Other countries connected by bridge or causeway (Denmark and Sweden, Saudi Arabia and Bahrain) aren’t shown as sharing a border.