That is not even true. The Septuagint does NOT say that Mesuhalah died in the same year as the flood. Read this for proof:
Under the sub-heading: Discordant Ages Of The Patriarchs In The LXX:
"In Chapter one, Floyd does speak of the discrepancies between the Masoretic Hebrew text and the Septuagint text, as far the length of years that some Patriarchs lived. However, he has a pre-conceived idea that, since the Masoretic Hebrew text is more accurate, that the Septuagint must be wrong. He does not consider the possibility that the Septuagint could be correct, and the Masoretic Hebrew incorrect.
One of the reasons he gives for why the Septuagint is wrong is because of the age of Methuselah. The Septuagint records that he was 167 at the birth of Lamech (Genesis 5:25), while the Masoretic Hebrew reads 187. Here is his reasoning:
“The majority of LXX manuscripts give 167 as the age of Methuselah at the birth of his son, Lamech (the Masoretic Hebrew reads 187 - Gen. 5:25). However, if Methuselah were 167 at the birth of Lamech, Lamech 188 at the birth of Noah, and Noah 600 at the Flood (as recorded in the LXX), Methuselah would have been 955 at the date of the Flood. Since he lived to be 969 (the life span given in both), the LXX becomes entangled in the absurdity of making Methuselah survive the Flood by 14 years! Yet Genesis 7-10 and II Peter 3:20 are adamant in proclaiming that only Noah, his three sons and all four of their wives; that is, only 8 souls survived the Deluge.”
It "seems" like a good argument! The only thing wrong with it is that Floyd is lying as to what the Brenton's edition of the Septuagint states! Both the Septuagint and Masoretic texts state that Methuselah died at 969 years of age; the Septuagint does not say 955 years old. Both manuscripts are in harmony with each other on this point. Floyd says the Septuagint records Methuselah being 167 at the birth of Lamech, Lamech being 188 at the birth of Noah, and Noah 600 at the Flood, which totals 955! Thus, he claims the Septuagint says Methuselah was 955 years old when he died. This is a lie!
In the Brenton's edition of the Septuagint, even though it does record that Methuselah was 167 at the birth of Lamech (Genesis 5:25), it records Lamech being 802 years at the birth of Noah (Genesis 5:26), and not 188 as Floyd claims it says. Therefore, 167 + 802 = 969 years old! Exactly what it's supposed to be. As a matter of fact, the Septuagint specifically states that Methuselah lived to be 969 years old in Genesis 5:27!!!
Therefore, Floyd's claim that the Septuagint records Methuselah being 955 is a blatant lie! The Septuagint says no such thing. Dear reader, you must not believe everything you read from those who would attack the Word of God. Please test these people, and read the Septuagint for yourself to see if it really says what these people claim it says.
After Floyd's blatant falsehood, in the very next paragraph he speculates as to why Methuselah's age is different in the Septuagint (which it is not); What is his claim? Because it is “a philosophy which embraced the basic precepts of evolution. That is, they were primeval evolutionists.”
So, here is Floyd accusing the writers of the Septuagint of being evolutionists! He comes to this conclusion on nothing more than his claim that the Septuagint says Methuselah lived to be 955! Yet, as is easily verified, the Septuagint says no such thing! The Septuagint says Methuselah lived to be 969 years old, just like the Masoretic Hebrew text states.
Not only is Floyd debating opinions of others about who wrote the Septuagint, but now he is digressing into his own opinions (based on a lie to begin with) about those "mystery" writers being evolutionists! Dear reader, God does not respect opinions and lies, but Truth.
So, since Chapter One mostly deals with people's “opinions” about the Septuagint, and misrepresentations about the Septuagint, I shall move on to Chapter 2."