From reading the excerpt, I gather that he is using the same method of reasoning that the Watchtower uses to bolster it's claim that mankind is only about 6,000 years old (despite archeological proof that shows otherwise). The Watchtower has it's own unique standards by which Biblical passages are interpreted. And thus, their methodology becomes the litmust test by which overyone else must read those passages also.
Case in point: the Watchtower discounts overwhelming archeological evidence that mankind has been on earth longer than 6,000 years. They claim that they "follow the Bible, rather than secular ideas". Yet why do they reject Genesis' clear statements that the heavens and the earth was created in seven days? Since they cannot retain any credibility by adopting the literalist view of the seven creative days, they have conceded that those "days" are undisclosed "periods" of time. But, that is not what Genesis says. And other fundamentalists have jumped on the Watchtower for arbitrarily picking and choosing what they will view as literal and what they will not.
The Watchtower is more than happy to accept the various archeological dating methods when those estimates confirm the historical accuracy of a certain Biblical accounts (conquer of Babylon, etc). But when those very same methods reveal human remains and dwellings that are much older than 6,000 years, they quickly reject it as "unreliable". They fall back on their same pious platitude that they "rely on the Bible instead of secular ideas". They want to have their "archeological cake" and eat it too. They clearly want to have it both ways.
We can see that the Watchtower has displayed a rank intellectual dishonesty over and over again with it's Biblical interpretations. Why should we believe them about the 587/607 issue? Are they not the ones with the most to lose if 607 is not correct? Emotional investments do not render the most sober minded analysis.