An award winning journalist and host of Russia's flagship national news programme was reportedly fired after this incident.
It sometimes seems like a different lifetime, but I too used to read the news, albeit only on a regional programme. This newsreader probably thought the director had already cut to the VT, so she was out of vision and her gesture was for the amusement of her colleagues on the studio floor and in the gallery, who'd see her on the preview monitors.
In my first day in training in 1982 I was told, "never say to a microphone anything you wouldn't want broadcast". That goes double when you're infront of a camera.