User blog comment:Xilinoc/Ch. 570 (I can't think of a witty title at 11 pm)/@comment-29183117-20140226133717/@comment-1268838-20140226144934

I think that's a likely explanation. The Royd brothers had rather modern-looking clothing as well. Plus I wouldn't find it very hard to believe that Quincy bloodlines continued to exist even after the massacre... the Ishidas might have just been the only ones to still have knowledge of the Quincy traditions.