Calf muscles (along with the muscles that make up the hamstrings and quads) do not instantly tear, contrary to popular belief. Tears\strains occur after a series of micro-tears build over time for various reasons. So, one can believe that a sudden hard sprint from the bullpen would cause the tear and it wouldn't have occurred had the incident not occurred (which supports this sensationalist crap that's been spouted the last two days) or one can simply come to the conclusion that the calf muscle was going to tear at some point in the very near future regardless (whether it was jogging in from the bullpen, finishing a follow-through on a pitch to the plate, etc.). I venture to think most former high level athletes, PT's, or sports medicine individuals would agree with the latter.
As for Travis, last I checked, he's day to day. If he plays tonight, the sensationalist argument will lose one of its two examples of why we should all be playing nice with the bloody Yankees. If he can't return, then yes, absolutely terrible to lose a player of his caliber in general, let alone outside of the general field of play. I, for one, will not jump on the hindsight train and cry tears over spilt milk.