When you add the "I'm afraid to say I love Trump" voters, that puts Donald at about 37%...
Merry Christmas!
You need to read more carefully. This is an automated phone poll, which means that there is no person on the line asking the questions, so your assumption has no merit in this case. Actually, automated polls tend to be LESS accurate because fewer people will respond, and the responses they do receive are harder to validate.
On another note, the last time this particular poll was done, it had Trump at 29% and Cruz at 9%. So this poll shows much the same trend as all of the other Iowa polls - Trump staying more or less steady, while Cruz makes a huge increase in support.