You did complete the first 4 years of graduate studies before 2016. This questions is specifically asking whether your bachelors degree was received before 2016.
See the following from IRS Publication 970:
Student qualifications. Generally, you can claim the American opportunity credit for a student only if all of the following four requirements are met.
As of the beginning of 2016, the student had not completed the first 4 years of postsecondary education (generally, the freshman through senior years of college), as determined by the eligible educational institution. For this purpose, don't include academic credit awarded solely because of the student's performance on proficiency examinations.
Neither the American opportunity credit nor the Hope scholarship credit has been claimed by you or anyone else (see below) for this student for any 4 tax years before 2016. If the American opportunity credit (and Hope scholarship credit) has been claimed for this student for any 3 or fewer tax years before 2016, this requirement is met.
