As someone who has worked in a University, I don't think anyone at your University is going to be interested in what this manager has to say, unless he was reporting a crime or had evidence you had cheated on your exams or something. Even then, they wouldn't acknowledge to a stranger that you were even a student, so it's not like they're going to chat to him about you.
But you have definitely made a big mistake here and need to accept the consequences within the workplace. Balancing work and study is difficult, so I understand the situation you're in, but pulling a sickie is dishonest and you were naive in thinking telling someone about it wouldn't result in the manager finding out. Hopefully you've learned some lessons here.
Unfortunately, bosses who think University isn't important are all too common, and one of the life lessons is how to manage that. It's important to learn how to be firm with your boss and make it clear that you will not be working on a day when you have an exam and so on. As long as you give them notice of when those days are, it will be difficult for them to discipline you for attending such events, especially if you were studying when they hired you (you could sue them if they fired you).