The philosophical works of Russell, Wittgenstein, and others in the Analytic Philosophy tradition of that era are still of great importance. Their ideal may have failed — they never managed to bridge the philosophical gap between logic and the objective world to produce the fully 'scientific' logic they had desired — but there is no denying that they made significant contributions to both mathematics and systematic logic. As the poets say (and every philosopher knows in his heart) we learn more by failure than by success.
Politically, however, Russell was an ardent dilettante social activist. See the wikipedia page on his political views. This is his assessment, not mine; he consistently tried to keep his philosophy separate from his political interests, to maintain the former's standing as insular and objective. His political views were passionate, but lacked the intellectual consistency and rigor of his philosophical work. Wittgenstein, by contrast, was largely disinterested in politics, or if he was interested, his interests were hidden behind his typically indirect, aphoristic writing style. Wittgenstein in his later years always aimed to subtly lead people to think through to conclusions; he avoided the kinds of direct, pointed assertions that are typical of political claims.
I suspect this particular quote is aimed at a less savvy subset of Russell's followers who conflated Russell's philosophy and politics. Put in less snarky terms, Wittgenstein is suggesting that Russell's philosophical work is unique, sophisticated, and important, while Russell's political work is garden-variety polemics that no one would think twice about except that they were written by Russell. Wittgenstein doesn't want Russell's legacy tied to the latter.
