In theory, you are correct. In practice not discounting the story of Noah as scientifically plausible would mean including it (and every other creation story that exists) on equal footing and demanding equal time in any geology textbook alongside the theories that we do have physical evidence to support.
No geology textbook has a shortage of regional floods which might, somehow, have been the root cause of the Bible's Noah story, or many others similar -- including "outburst floods" in the Persian Gulf and Black Sea circa 6,000 BC.
These were certainly large enough floods that people of that time might well have considered them "worldwide".
And, by the way, while we're discussing this, in the King James translation, Genesis 7:20 reads:
Of course, other translations put it differently, but I read this one to say the waters rose "15 cubits", which is roughly 23 feet.
Now, I'd say a flood of 23 feet in the regions of the Tigris, Euphrates and Persian Gulf is entirely realistic, but then the point of the story would be negated, wouldn't it?
So here is a case where a "literal" translation of the bible is necessarily rejected in favor of a more, ahem, metaphorical understanding, right?
;-)