At the time he took the exam in the 1960s, the exam may have consisted entirely of essay questions. With an outline of each area of the law memorized, and some practice in writing essay answers in the style required, it may not have been that difficult to pass the exam if the exam at that time had a 50 to 75% pass rate. He was obviously a very intelligent man and he was very observant. He undoubtedly had a great memory. These days, the multistate portion of the bar exam would make it more difficult to bulls*** your way through the exam.
A big portion of succeeding at the bar exam is time management, and another big portion is raw intelligence. You don't have to demonstrate Perry Mason type mastery of the material, because there just isn't time. The essay format separates those who know too little from those who know "enough". The multiple choice questions that are on a modern day exam do a better job of identifying those who simply haven't studied enough.
Some state bar exams are a lot tougher than others. The Louisiana bar exam was probably fairly easy to pass back in those days. When the bar exam is only offered twice per year, you are under tremendous pressure to pass on the first try. If you know that you can re-take the exam over and over until you pass you just aren't going to be as motivated to study day and night. So Frank's competition might not have been so stiff back in those days.
What I wondered was WHAT Frank studied to prepare for the bar exam. Were there review books available back then??? He must have gotten some advice from somebody on what he needed to memorize, etc.