UnitedHealth Group Inc. said a hospital error led to its phone call with a Texas surgeon that was later criticized by billionaire Bill Ackman, who suggested that the insurer overstated profits in a since-deleted post on social media.

UnitedHealth Group said on Wednesday a mistake at the hospital was behind the phone call that led to a surgeon being pulled from the operating room to defend a patient's inpatient stay, a move that was eventually criticized by billionaire Bill Ackman.