"Is that a thing?"

While Grant and Martha did an admirable job of tracing references to "a thing" (any significant cultural concept) and "[just] the thing" (that which is in fashion), I have to wonder if the usage the caller asked about was influenced by the earlier "it's a thing; you wouldn't understand" (you'll never fully grasp this because it's part of a culture you don't belong to). Seems to have started first with "a black thing" (sometimes "thang", to add a dash of dialect to the expression), then expanded to "a Jewish thing", "a guy thing", etc as needed.