Not having seen the actual video to know for sure what she is referring to, I would be guessing that having her throat fucked would be the most likely cause of the breath restriction.
The position would make it difficult to breath, but not impossible. However, combine that with a cock plugging her throat, liquid's natural tendency to flow downward and she would be having a serious problem getting air into her lungs if the guys weren't paying attention, especially if she gagged or vomited.
