Even coaches can make errors in their own training.
In my case, I did a hard race-pace session with a lighter pair of shoes than I normally had been. That along with not actually doing many workouts like this lately due to snow/ice/etc meant that my calves really took a beating.
For the last few years, I have had a quarter sized area on my left calf that has been my only real problem area. Well, the problem area is my brain not being mindful enough to know such a workout was going to overload my calves, but that is another discussion altogether.