Trump did not acknowledge that Russia was being any hacking. What he said was something like 'I think it was Russia... but it also could have been someone else.'
It was likely an expression to placate impressions that Trump is a lackey of Russia - as I think Rex Tillerson is also making an effort to do with his own measured, though open-ended statements concerning Russia, and the new administration's approach to Russia. They're trying to have people not think the new government has already decided what it wants to do regarding Russia, and to avoid any appearance of being an open door to Russia. They're trying to establish their own credibility in the eyes of their detractors and potential detractors, by using measured statements.