Lol the angle in that story is that Democrats should "give up" gerrymandering to convince Republicans to do so. I don't think this counts as "pro-Republican" (or "anti-Democrat")
bias.
The point is that it draws attention to Maryland, which is gerrymandered by the Dems - contrary to your claims that they'd ignore that. Why is it supposed to be "pro-Republican"?
(Nor is it the only story NPR has on gerrymandering in Maryland, by the way - merely the most recent one.)