How to prevent double calls

[PWL]

I don't know if anyone remembers this play from the AL playoff a few years back. Miguel Tejada of the A's was just reaching third when he was obstructed with by the Yankees third baseman. Instead of running hard all the way home, Tejada started running about half speed and pointing back at the obstruction. As I recall the PU gave the out signal as the tag was applied at the plate. The U3 made the obstruction call. Nobody seemed to get too worked up over that as the call was the correct call to make. However if the PU knew the runner was obstructed with, why was he making an out call?