Not necessarily. Simply believing that Cruz is ineligible for the Presidency doesn’t mean that they still won’t vote for him.
The right way to figure that out is to ask a followup to that 25% asking whether they’d still vote for Cruz as the nominee.
And then there are positions candidates hold that are unconstitutional. If a candidate holds enough of those positions then a voter may decided that they are "ineligible" to hold the office and not vote for them.
For example a candidate like Trump who is for affirmative action, Kelo, universal health care, government bailouts and stimulus packages, all that unconstitutional nonsense.