You have seen it now :).  I would say that this use of underscore as a throwaway implementation variable name is a fairly common idiom.  Also temp is bad variable name because it collides with the use `temp` for temperature here.  Also there are many people who feel that temp is a bad name in general because it provides no semantic meaning.

If anything I think that we should update the style guide to say that temp is reserved for temperature (in Kelvin).