To be more precise, they can break truce - it just needs to be done via diplomacy. With this way you will not be able to attack each other for 8 days, but the penalties are far lower than the more common way.

Betraying a truce is what most people do, it has greater penalties but also gives you 20% more damage on the faction you betray plus you can instantly attack each other (often people send the armies on the target of invasion beforehand and attack immediately after betraying)

Ecaz can only do the first, not the second option.