Wrong.
en.wikipedia.org/wiki/Mammalian_diving_reflex#Effect
"Mild bradycardia is caused by subjects holding their breath without submerging the face within water. When breathing with face submerged this causes a diving reflex which increases proportionally to decreasing water temperature. Activating the diving reflex with cold water can be used to treat supraventricular tachycardia. However the greatest bradycardia effect is induced when the subject is holding breath with face submerged."
Your comment was incorrect though, you attributed an effect with a specified cause to a different cause, with the obvious implication that the previously specified cause was untrue.
en.wikipedia.org/wiki/Mammalian_diving_reflex#Effect
"Mild bradycardia is caused by subjects holding their breath without submerging the face within water. When breathing with face submerged this causes a diving reflex which increases proportionally to decreasing water temperature. Activating the diving reflex with cold water can be used to treat supraventricular tachycardia. However the greatest bradycardia effect is induced when the subject is holding breath with face submerged."