the article clearly stated they all left it was inhabitable..meaning you couldn’t grow Food! it was a marsh in warmer period!
And you derived from this that Greenland was completely flooded exactly how? My father's farm in Missouri is a marsh in the Spring, that doesn't make it flooded.
Besides which, people didn't come to Greenland until 985AD, which was during the warmest period in the last 2000 years. All of those settlers' decendents were frozen out of Greenland by the Little Ice Age and were completely gone by 1500 due to the cold climate. So your "warm period" exodus (c.1600) doesn't make much sense.