What a crock. Only one calls the toss. Have you ever actually done a coin-toss?
If you want to be pedantic, neither of them call the toss-- neither candidate was even present. The county clerk of elections both flips the coin (or designates the person who does so), and calls which result goes to which candidate (or designates the person who does so). If the clerk calls heads for one candidate, they are calling tails for the other.
That's the way coin tosses work: calling heads one way also means calling tails the other.
What I find more puzzling, and probably more worthy of attention, is that the media almost instantly put out the story "Hillary won six out of six coin flips"-- but the best reported actual data is that, of the coin flips that were officially recorded, Sanders won five out of six against Clinton, and one out of one against O’Malley. (e.g., this report).
So, was it just coincidence that the media happened to get 6 out of 6 data points about Hillary winning coin flips against Bernie, but zero out of six data points about Bernie winning coin flips against Hillary? What are the odds of that? Well, the same calculation.
The original six out of six number apparently came from the The Des Moines Register, who based their reporting on what had been posted to Facebook (!). In a later story, they stated that the actual found of coin flips was "unknown".