the partial pressure of helium in the atmosphere is minimal (about 0.0005%), and the amount in the lake water would be even lower, making helium infiltration un

the partial pressure of helium in the atmosphere is minimal (about 0.0005%), and the amount in the lake water would be even lower, making helium infiltration unlikely to be a significant factor. my extremely unqualified opinion is that water seeped in through the cork, but the cork was still fairly well lodged in place, so it had the high pressure of being 15 meters down despite not being originally bottled at pressure, and when brought back up, the glass shattered instead of the cork popping out