The more charitable, and arguable more correct, interpretation is that there are (at least) two related but distinct meanings of 'Bayesian' being used. One is referencing Bayes' Rule and some of its implications; the other an entire sub-field of statistics. I'm guessing there isn't much overlap between the two groups of people.
It also certainly doesn't seem impossible to be, e.g. "an expert on classical literature but [not] know how to read greek/latin". Surely there's a lot to know about classical literature that isn't strictly pertinent to the actual vocabulary or grammar of ancient Greek or Latin. Or are you claiming that there's only one right way, or only certain right ways, for someone to augment their primary expertise with ancillary knowledge? I haven't previously encountered the idea that being a polymath implied expertise in numerous areas, just knowledge, tho presumably more than most laypeople.