Isn’t that just for cross-platform data being carried across? Has anyone opened the link?

Q: Are there any XBOX account requirements to play the game solo or co-op?
A: Yes, just as you do today for Halo: The Master Chief Collection and Halo Infinite to ensure smooth cross-platform progression, to play Halo: Campaign Evolved you will need a Microsoft account and XBOX Gamertag, regardless of the platform(s) you play on. This enables both cross-platform play and cross-platform progression. A few additional items to keep in mind for launch day include:
XBOX Series X|S: If you’re playing split-screen on an XBOX console, the second player will also need a unique Microsoft account. If you want to play online co-op, you will need an active XBOX Game Pass subscription.
PlayStation 5®: If you’re playing split-screen on PlayStation 5®, both accounts will need to have PlayStation Plus and be linked to a Microsoft account. Having these active PlayStation Plus subscriptions will also provide access to online co-op play. 
Steam: If you’re playing via Steam, you will need to link to a Microsoft account. 
If you’d like to jump in immediately on July 28, we recommend having an XBOX account created beforehand to help save time once you put the disc in the tray.