The wording is a bit ambiguous, what I believe they meant to say was that if the Attacker fails to differentiate between the Technomancer and his Proxy, then the Attacker targets the Proxy with a Matrix Action. The Technomancer rolls a defense test as normal. If the Attacker succeeds, the Proxy disappears, and Technomancer takes no negative effect. If the Technomancer’s defense test succeeds, the Proxy remains because the attack missed.