Usually, poor form, too high poundage bow, too long draw or combo of all.

Tell your "friend", to hold out his hand/arm to his side in a natural relaxed position. Thumb not pointing up or down but dead natural. This is how the bow should fit in the hand. If he has to dig his heel of his hand, string can hit. If he has his elbow turned in, poor form.

Problem with too much wieght is usually a shooter has to dig the heel of his hand in to control the bow.

A proshop should be able to get him on track in no time.