Perhaps the Yahont carries its own ECM, thus the need for data on the adversary's (US) ECCM systems on board? What the description said was that the missile carries ECM and ECCM data in its memory, as well as the means to evade "the enemy's air defense systems". I can't see why it'd need ECCM data if it didn't have its own active ECM.
Like I said, perhaps you're paying too much heed to the manufacturer's brochures.