The parts with Joey on "Pyramid" were shot on the "Pyramid" set. The "Pyramid" audience got a big surprise when they thought they were there to watch a real game of "Pyramid" but instead got to watch the taping for a "Friends" episode.
Ross makes mention of a number of different people that he would like to see while at the reunion, one of them being Michael Skloff and another being Jeffrey Klarik. Michael Skloff is the co-writer of the iconic Friends (1994) theme song as well as additional music for the run of the entire series. Michael's wife, Marta Kauffman, was a co-creator of the series as well as a co-writer of the aforementioned theme song. Jeffrey Klarik is the lifetime partner of co-creator David Crane.
The wide-screen version of the episode has the "on-air broadcast TV screen" version of the game show portions in academy ratio (3:4) with black sidebars on left and right. The in-story non-broadcast studio sections are in the wide-screen film ratio, as usual for the rest of the entire run of "Friends". This is perfectly logical, as Warner Bros Television knew the future planned wide-screen ratio would be 16:9 eventually, and were future-proofing all of their Filmed Programming. Conversely, as "the Pyramid Game" was actually already being video recorded on 3:4 video, the onscreen graphics wouldn't have been designed for wide-screen that early in the wide-screen broadcast migration plan, as gameshows were considered fairly disposable. Remember this was before game show themed channels such as the Game Show Network and Challenge TV.