When reading Isaiah 7, I think their claim is fairly accurate. One of the biggest pieces that stood out to me is that this chapter is written in third person. Isaiah is not speaking for himself (7:3 "Then the Lord said to Isaiah..."). Looking at the chapter immediately before and after, Isaiah is talking in first person. This to me is a clear indication that this has been edited or added after the fact. With this thought in mind it would be easy to see that the author has taken what was written in put it in more contextual terms that the people of his time would better relate to. Taking information from Collins (page 215), that "...the phrase "on that day"...are usually though to be editorial additions", leads me to believe that these are things that were added later to make the passage more relatable to the time it was edited. I am not great, yet, at being able to align historical data with scripture, but it seems as though the person editing this section is trying to offer hope for the future. In reading the need for hope of the future gives me the impression that the people are already under siege or exile. There is hope of being able to back in the promise land and that the places they are coming from will be turned into lands no one could farm nor live. If they were already living "safely" in a land of plenty they wouldn't need the hope of a future fruitful land.