I came across this story elsewhere and stopped for a brief moment. It is not likely the teacher said anything. The father said he did review instructions "on line". He also said, "but the teacher said" and the teacher said "nonsense.
I notice the stopper is cork. All the science calculations are not really necessary. Cork - and I'm just guessing, can sustain - ohh - maybe 1.4 atmospheres - probably 25 - 30 psi depending on the side of the opening. To keep this as confusing as possible lets use a 50 cigar ring diameter.
I'd say a lack of attention got 3 kids burned.