Using of "be" in an irreal situation.
In order to expand my vocabulary and entertain myself at the same time, I read the entire saga "A song of ice and fire" by George R. R. Martin. In one chapter I found this sentence - "...shit on your wolves and giants, he would piss his pants if he knew we was coming." My question concerns the second part of the sentence, namely "if he knew we was coming." Shouldn't a character say "if he knew we were coming"? Is there an error commited by a simple soldier or a particular difference in use of the verb "be" in the irreal past? I appreciate all your help.