Fisherman -
Non sequitur, WT has never taught that the truth of God's word has ever changed and neither does the attitude that they comment on referenced in your post represent that of JW.
They have themselves changed the Bible, deleting certain scriptures that they had previously included in their bible is just one example.
Quote from JW org re Truth - They hold that truth—especially moral and spiritual truth—is not absolute but relative and ever changing.
They hold to this view by their ever changing doctrines, both in re-interpretations and flip flopping on ideas.
This, of course, implies that people can determine for themselves what is right and what is wrong.
This is what they conclude when there is ever changing truth. They get to choose what is right and what is wrong by their own interpretations. There are many examples of them changing their minds about what is right and what is wrong, I am sure you are familiar with some of them.
As for truth from God's word, that doesn't change.