At some point back in ancient times a man laid on his back with his legs in the air, his hands wrapped around the bottoms of his feet. And his wife frowned down at him and told him he looked like a "dead bug", thus the posture was named.
At some point in the American yoga revival of the 20th century, peace loving practitioners of the ancient pose thought dead bug was too violent of an image and so renamed the posture "happy baby".
And one morning during 5:30a.m. awakening yoga, in a small town in Wisconsin, an instructor inadvertently mixed the two names and unfortunately, the result was not "happy bug".