Well, plenty of Trump supporters probably stopped reading that paper because of their anti-Trump bias, which means they didn't know the paper was doing a poll and thus didn't vote in it. Maybe the Cruz camp saw there was a poll for that paper and got all of their workers and volunteers to vote, easily skewing a small poll. I don't think that the paper fudged the numbers, just that they happen to be polling a small group that is itself favors Cruz or Trump.