Actually, it probably was the cutter then.
Osuna has thrown 10 of his career 16 cutters since June 9th. Looks like he's trying to mix it in more.
http://www.brooksbaseball.net/tabs.php?player=532077&p_hand=-1&ppos=-1&cn=200&compType=none&gFilt=&time=month&minmax=ci&var=gl&s_type=2&startDate=03/30/2007&endDate=06/29/2016&balls=-1&strikes=-1&b_hand=-1