They probably meant that it needs a hole in it so it does not act like a faraday cage - I assume its metal. The glass probably is just a cosmetic choice of material.

Meridian owner since 1992
Prime & PSU, Focal Elear headphones, Roon (ROCK 8Gi5 NUC), Explorer 1 & 2, F80. 200/203, various Sonos (via Roon).