I think you are misreading something. Most of Greenland (not counting ice) is well above see level running from hundreds of feet to thousands of feet. If all the ice in the world completely melted, it would only raise the sea levels 150 feet.
So how did Greenland get completely flooded c. 1600 AD without also flooding all of Florida and most of Southern England?
I think you are reading about one particular area of Greenland where warmer wheather turned the permafrost into mud.
the article clearly stated they all left it was inhabitable..meaning you couldn’t grow Food! it was a marsh in warmer period!