Cruz was Bush’s domestic policy adviser in 1999.
Proposition 187 was still talked about a lot, and Bush wanted to have a policy statement on it.
http://www.nytimes.com/interactive/2015/12/18/us/politics/immigration-document.html
Bush disagreed with it in 1994, he said so. He was asked about after he was elected Governor, before has was sworn in. Long before Cruz went to work for him in 1999.