Being a naive tool is the more innocent hypothesis.
One of the hacked emails from campaign chairman John Podesta contained apparent transcripts of Clinton's private speeches, where she advocates for "open borders and free trade," which her campaign later downplayed as a generalization of her views on trade. Trump, though, seized on the email to press his case against illegal immigration.
Hillary and Rubio are on the same page on immigration and the Davos vision of a world without borders.