Wow!
You just made me feel a whole lot better about this poll.
How quickly did they conduct this poll? There is a lot of pressure on interviewers to get completes. This is especially true, when the poll has to be done quickly.
A scenario where the interviewer puts the respondent in the poll, whether they say they were registered on not, is not hard to believe. I've seen it.
A percentage of the calls are supposed to be monitored by the shift supervisor, but time pressures lead to problems with the results. That's a fact of life in the research business.
Having done some telemarketing in the past to get people to try to come to focus groups, I can tell you there is a great deal of pressure to find respondents. In our case, we bent the rules or led the person we called on a little bit to get them to say they were a user of a certain product or whatever.
I would think there would be a lot of pressure to take a person at their word when they say they are registered. I think there is also an "embarrassment factor," where people don't want to admit they aren't registered, plus an "importance factor," where people who know they won't be eligible to give their opinion lie about their registration status so they can. (and feel important).