A Whoa! Whoa! Wait a minute... at work

The other day I found out that a superior at work said to her employee after explaining something that this employee would never understand because she did not have the proper training to understand such stuff...."are you stupid?" Whoa! Whoa! Wait a minute....This not only is uncalled for, but for a superior to say that to an employee...WOW!! If it was me I would have gone straight to HR....I hope that is what happened in this case.