flip backward

The correspondent of Sports Illustrated wrote: "Larson, a tall and fiercely competitive blond, was victimized by the confusion of tongues that prevails at all Olympic Games. 'Did I win? Did I win?' he shouted from the water, and one of the foreign judges beamed at him. Larson thought it was a smile of congratulations - it probably was amusement over his boyish eagerness - and flipped joyously backward, kicking off in a long glide to celebrate what he thought was victory. And so thought the crowd, which cheered him. Then the official decision was announced. A few minutes later a grim Larson stood on the silver-medal level as the band played God Save the Queen and Devitt received the gold medal.

what is beam at
and his means whose?