The problem with using puddles as your method of transportation is that occasionally, someone cleans up a puddle. Some member of the janitorial staff was on top of their game and mopped up the puddle that Strange had used to go back and ditch the concert hall. So, he decided to go back to one of the few mirrors he knew were backstage and knew couldn't be removed from the wall. He wanted to get the heck out of here before the singing started, after all.

It's at this time, as Strange is moving towards the dressing room location he knows, that Strange almost gets a fireball to the face. He puts up his own hands, starting to mutter a counterspell, but stops once Rita extinguishes her flame. She doesn't sound sorry, Strange doesn't sound happy. He can't help but frown slightly at Rita's excuse.

"And what, you'd charbroil them? That would certainly stop the concert."