I was not suggesting ULD's are pressurised, but if it was sealed (which it is not, as has been explained apart from fly away kits which are secure all metal bins with locks, or cooled containers) that in a rapid decompression, it would have the potential to be of a higher pressure than the ambient pressure environment around it, which could lead to a rapid equalisation, through a weak point.
However, if the canvas flap just flaps open, then a non event. Hence my apology.