I agree that "anyone with guarantees/in a faction with CZE gets an event" -- but in this case, Romania was Faction Leader, and that's where the difference lies. Faction Leader makes the call in the negotiation. Sure, Czech AI (or role-playing gamer as Czech) could still reject the deal (if the Faction Lead gave away their land - although I would not have, as Romania/Faction Lead), but if for arguments sake Czech did reject - they could withdraw from the Cordon Sanitaire and then fight Germany solo (not a logical choice whatsoever).
The more important thing that should change in the game is the specific authorities that Faction Leaders should hold for these negotiations, rather than just having yet another pop-up event fly by that affects a member of their Faction/Alliance.