This verse appears to be a textual transmission error — the description corresponds to other postures, not to Mayūrāsana which is an arm balance. In more complete manuscripts, the description of Mayūrāsana is different.

Classic Mayūrāsana is executed: supported on the forearms with the elbows at the abdomen, the legs extend backward and the body is lifted horizontally. It is a plank on the arms.

The posture strengthens the abdominals, arms, and develops exceptional balance. The pressure of the elbows on the abdomen stimulates the digestive system.