It doesn't matter that McDaninel was never a majority vote winner. --
Good catch, and I agree that McDaniel need not ever have obtained a majority of the votes cast; but, the primary was a three way race. If Cochran had dropped out before the runoff, then there still would have been a runoff, unless the third candidate (name escapes me) also dropped out.
Thomas Carey got 4,789 votes (1.5% of the total). Compared to the > 150,000 votes that both Cochran and McDaniel got, I doubt that Carey would choose to participate in a new run-off, unless he's just a glory-seeking spoiler.
-PJ