I can offer an explanation, but I am unsure if the mechanism I propose is the one that produced this use.
If others have better proof, I will be happy to see more answers.
Consider the previous weekend — assuming you are reading this on a weekday.
It is the newest weekend of all the weekends there have been so far.
It is also the last weekend so far.
One can see "newest", "last", "latest" and "previous" as synonyms in this context.
(In this context "last" does not mean the last of all weekends there will ever be, but in your quote "last" does mean the last of all nights.)
Due to situations like this, one might learn to identify "newest" with "last".
Once these words are identified, they can be used synonymously even in cases where the original reasoning makes little sense.
My "weekend story" above gives no reason say that "newest" and "last" are always synonymous, but extension of an analogy beyond its original realm is not that rare.
Since in your quote "last" and "newest" do not seem to mean the same, this kind of mechanism sounds plausible to me.