"Rosenstein’s message may have been based on a technicality. Trump may not officially be a target, but Mueller hasn’t ruled out making him one at some point in the future, according to a U.S. official with knowledge of the unfolding investigation."
Take a moment to read this:
http://www.foxnews.com/politics/2018/05/01/muellers-questions-for-trump-read-full-list.html
There are plenty of questions in there about obstruction.