Makes sense to me: while performing chest compressions, air is automatically exchanged in the lungs via the intrathoracic pressure changes. Think: when someone gets hit in the gut/chest, they make a "ugh" noise: this is due to air being forced out of the lungs via a "chest compression". Being an ICU nurse, I have performed CPR many times and am witness to this.
It helps to ensure the head is tilted back to keep the throat open. Thanks for sharing this link.