Well in content-single.php that is just another call to it using functions as parameters. It is not the function itself.
It may well be the case that the fault is in your functions file but I've looked and can't find anything glaringly obvious hence my suspicion about the file that contains this function.
Usually, unexpected errors usually mean the line above or below. In your functions file those are both ok hence my suspicions.
You really need to use the undo option on your editor and go all the way back to the start..