I've seen this sort of thing play out before. If you engage them in good faith, they'll ask for a source on your claims, only to dismiss it and demand a different source that agrees with them. Sometimes they are willing to listen, but sometimes they come in and open with smug condescension and only get worse from there, their goal is to suck up all the oxygen in the room and waste everyone's time. Once they're clearly doing that, a quick and succinct PPB gets them to leave.