I read this from Living with a Black Dog by Matthew and Ainsley Johnstone:
When I initially handed over I Had a Black Dog to my publisher in 2005, I emphatically stated that I didn't wish to become the poster boy for depression; this was part of me, not the sum total. Them fighting words were my way of dealing with the pending fear that comes with launching something deeply personal into the public arena.
What does "them" refer to in this context? The words the writer wrote in I Had a Black Dog? Or what he emphatically stated to his publisher?
The use of 'them's fighting words' is a folksy, colloquial expression, said when someone makes a statement that the listener takes strong exception to. It probably won't actually provoke a fight, but indicates to the speaker that they need to 'back off', not pursue the idea they have expressed; and even apologize.
The ungrammatical use of 'them's' for "those are" is first recorded in Ring Lardner's Gullible's Travels (1917). In your quote, it's referring to a past situation - just like you say 'those are' for the Present tense, and 'they were' for Past - and the Johnstones therefore have to change the saying to "Them fighting words..."