Can’t say. The melting of the N America glacial cap happened in stages over about 4000 years, each stage raising the world ocean level 100-200 feet suddenly due to collapse of ice dams. These events were roughly 9000, 11000, and 13000 years ago. The story in this article doesn’t fit this sequence well if at all.
I think your 9,000 year date is too long ago. It should be closer to 8,000...even 7-8,000 years ago perhaps.
THere were probably several times when the sea level increased permanently by feet or meters. If indeed a boloid event caused major disruption and tsunamis 13,000 years ago, this would have become part of oral history for many generations. Although the Agassiz even would only have raised the worlds oceans by a foot and one half; first, since the water flooded into the North Atlantic and the Caribbean very suddenly, it may have caused tsunami type conditions striking Europe and North Africa. The initial increase in water level would have been on the order of one or two meters before the levels settled down world-wide, not to mention possible much higher tidal surges (tsunamis).
With an oral history of other significant rises, coastal and marshland peoples might have considered it prudent to move the settlements inland permanently.