Last night they showed an audience as Alex was walking in, and Johnny pointed to Alex before clapping.
That was likely taken from prior tapings with full audiences (as Wheel had been doing), or they simply focused on the taping's remaining contestants and their guests.
Also, Johnny does not announce every episode in the studio. Roughly half of them have stand-ins doing the announcer's work with Johnny dubbing over them later. Usually it's done by the guy from the Clue Crew, and sometimes Wheel of Fortune announcer Jim Thornton does it as well.