Earlier quoted context omitted.
This [1] explains Sound Transmission Class (STC) ratings. > An STC label delineates how partitions and walls effectively block sound and reduce noise. Ratings are determined by broadcasting a specific auditory tone near the material, and measuring dB on both sides. The higher the STC value, the better its insulation. From the table STC=25 means "Normal speech easily understood" and STC=50 means "Shouting not heard" T…
I wonder if somebody vaguely remembered the effects of helium fill, which actually does reduce sound transmission, and vaguely remembered that argon-filled windows are a commercial product, and conflated the two because they're both noble gases.
They didn't even start with museum-grade glass for optimal filming, which to a absolute layman like me seems like they just hadn't bumped most of these problems before.