That doesn’t mean it represents what those people think, it means that they chose a group out of the 40% of people under that age who would answer their phones when an unknown caller calls them to poll them.
Maybe the poll is accurate, but I am very dubious of any telephone poll’s accuracy at this point because so many people simply will not respond to an unknown caller.
Focus group polling might be more accurate because you can pick the demographics ahead of time, but I don’t know.