Well, F2 is always a fielder: that's what the F stands for. The fielder's status doesn't change after D3K, only the batter's status changes (now a BR).
Also, umpire INT is always with a fielder: INT is hindrance of the defense.
Moreover, look at the definition of umpire INT. The relevant part of FED's says: "inadvertently moves so as to hinder a catcher's attempt to throw..." It's not restricted to a batted ball, nor is the status of the batter/batter-runner relevant.
Finally, what's the purpose of the umpire INT rule? The fact is that the PU has to be back behind F2, and sometimes, hopefully rarely and always inadvertently, we get in the way. When we do, we put the defense at an unfair advantage. We need to acknowledge that and deal with it as prescribed by rule, not ignore it.
I will add that I'm assuming that the umpire hindered the throw, or attempted throw, and not F2's attempt to retrieve the pitch in the dirt. The latter, as a glance at the definition should make clear, is not umpire INT. We ignore such contact: if F2 falls down trying to get the ball because he bumps the umpire, that's nothing.
That interp sounds as if it is from an umpire who doesn't want to get yelled at for the INT, and is rationalizing an incorrect no-call.