There is high chance that the 21K+ bitcoins are spread out over multiple wallets. Most likely hardware wallets, spread out over multiple geographical locations. I also don't see what the benefit would be for MicroStrategy to publish a csv files with all their wallet addresses.
Even more likely a custodian like Coinbase or Gemini already has the funds in cold storage, and a sale occurred OTC which simply modified who owned how much of the BTC.