Episode 21 of All-In with Chamath, Jason, Sacks & Friedberg (“Media misalignment, subjects controlling narratives & more with bestie guestie Draymond Green”) is indeed the next episode after E20 and it does contain a “Mean tweets” segment. However, multiple official episode descriptions and show notes indicate that:

• The episode opens at 0:00 with “Discussing Sacks’ recent hit on Tucker Carlson.”
• The “Mean tweets” segment does not occur until 1:08:02, near the end of the episode.

This structure is documented in the show notes on Libsyn (the podcast’s own host), Apple Podcasts, and Storytel, all of which list the segment order and timestamps, including “1:08:02 Mean tweets.” (allinchamathjason.libsyn.com) A separate summary/transcript view of the YouTube upload also shows a standard intro and banter at the beginning, not mean-tweet reading. (glasp.co)

Chamath’s prediction was that episode 21 would start with the hosts reading mean tweets. While they did eventually read mean tweets in that episode, they did not open the show with them, so the prediction—as stated—did not come true.