Trump didn't "open" this plant. Apple *has* just broken ground on a new campus in Austin, but the plant he visited -- owned by a company called Flex, not Apple itself -- has been producing the Mac Pro since 2013. Here's the article from 2013. statesman.com/article/201312… 
Trump has now falsely taken credit for the existence of three plants he has visited this year: one in Texas, one in Louisiana, one in Pennsylvania. It's his standard bit when he visits a manufacturing facility.
Per the NYT's @jacknicas, Trump was making similar claims this afternoon while at the plant itself.
