If accepting universals made one not a materialist, that would rule out some of the great Australian materialists, such as David Armstrong. Thus, that would clearly be a non-standard use of the label "materialist." Perhaps there are details of Russell's account of universals which are not shared by Armstrong's which make it anti-materialist, but you don't specify any. I know that Russell's views changed over the years, which of course complicates things, but he certainly didn't believe in spooky souls, and most of the doctrines of his I can think of which seem to be in possible tension with materialism are either susceptible to varying interpretations or matters he changed his mind on at different points or both.