I'm not Wiz but that is incorrect, many times you have an RFD with no tornado, and vice versa. There was a theory that correlated tornadogenesis with RFDs, and certain kinds of RFDs in particular, but the latest in detailed computer simulations suggests the RFD is more a consequence of the tornado then a cause (look at Dr. Leigh Orf's work).
Edit: Phrased that badly, did not mean to imply tornado causes RFD, as noted the two phenomena occur independently sometimes