The key here, I think, is that there are certain statutes (usually, but not always coming under Title 28 of the US Code) which are relevant to civil procedure: often they define the jurisdiction of the federal courts, govern when a case can be removed to federal court from state court, or (in the case of section 1391) determine issues of venue (i.e., in which federal district of a state can or must the case be brought, if there is jurisdiction there; that's another can of worms entirely). But these are statutes, which are nominally different from the Fed. R. Civ. P. (although the latter have the force of statute under the Rules Enabling Act, so for many purposes you will analyze them in the exact same way).