This works on the same principle as JUG. Anytime you are allowed to press G, the game state-checks you to see if you are standing or crouching to allow you to JG. In this instance, Astaroth 22B never hits during the "stun" of 22K, it always hits during the "getup" animation portion of it. That is normal for the combo.
The reason this attack can be JG'd is because during the transition from grounded state to "tech" state, there is ALWAYS 1 frame of standing/crouching, as a transition. It works the same as going from Aerial State to Grounded State (which is why the Sigfried backthrow trick works).