Not really hard to believe... a huge chunk of the calls will be voicemail/answering machines. And then once they get a hold of a live human, it may be a kid or someone who doesn’t speak English. After that, there’s only about a 10% or less participation rate.
Most people hear “Hi, I am Fred from Gallup...”
The pollster then hears: < Click, Dial Tone >
Unless my math is failing on me, that's a 3% participation rate.