1. UCP internal party politics are quite secretive. People knew that special interest groups like Take Back Alberta were calling the shots, but the fact that they were fully in support of separation was not known.
2. Smith has a Steve-Jobs-level reality distortion field. She can make insane things sound downright reasonable. There were and are people who listen to her and believe she is the staunchest federalist out there in spite of her actions telling a completely different story.
3. The Wildrose takeover was relatively quick and recent, while many voters tend to be not up on the latest news. Others may simply not have believed what they were hearing.
Next election, we'll see. It's pretty much impossible to ignore the fact that non-separatist parties generally don't go out of their way to hold separatist referendums.