Triggering "On Cast" Effects When Sacrificing
You should not have gotten a token


  601.2h Once the steps described in 601.2a–g are completed, the spell becomes cast. Any abilities that trigger when a spell is cast or put onto the stack trigger at this time. If the spell’s controller had priority before casting it, he or she gets priority.


601.2a-g are the steps of announcing the spell, choosing targets, paying costs such as sacrificing creatures, and so on. By the time the "casting a spell" occurs, Young Pyromancer is no longer on the battlefield and its ability would not trigger.