When a helium balloon pops, the sudden release of pressurized gas inside the balloon can cause a drop in temperature. This rapid cooling effect is known as the Joule-Thomson effect. If the surrounding air is humid, the sudden temperature drop can cause the moisture in the air to condense on the inside surface of the balloon.
The formation of a snowy layer on the inside surface of the popped balloon could be due to the condensed moisture freezing. The extremely cold temperatures resulting from the rapid expansion of the gas can cause the water vapor to solidify into tiny ice crystals, resembling a snowy appearance.
Without further information or the ability to examine the picture, it is challenging to provide a more precise explanation. If you have any additional details or if there are other factors involved, please let me know.