It is possible for them to coexist. I personally believe that Dr Pimentel jumped the gun on this one. Important research, but a little to quick to promote the "cause" before the research was done, in part because the testing wasn't that accurate to begin with, which again is really complex, not just for IBS, because of condition like Lactose intolerence and fructose and other issues. They did also know that people had sibo and din't have IBS. That made me go Hmmmmmmm?
The press also had a role in it, by jumping the gun, before more research was done.
There are symptoms sibo causes which are red flags to an IBS diagnoses, IBS does not. But it can mimick some symptoms of IBS, so the awareness about it was important as well.