What can you do when it's your truth vs. someone else's? Nothing, really, especially if the other person is your boss.
It's complicated when your boss makes a mistake, and instead of acknowledging and accepting that he did wrong, he tries to blame you for something you didn't do. In this case, they forgot to schedule the employee for a couple of days, so he didn't go to work. He's a student and really took the time to focus on finals. He texted his manager regarding not being scheduled, but didn't receive an answer. So he assumed that he wasn't needed.
A couple of days later, the manager called the employee to his office and handed him a document that was essentially a write-up for bad behavior. He was blaming him for not coming to work for a couple of days. The employee was confused and showed him the text messages he had sent, but the manager still tried to push the blame onto him.
The employee, of course, refused to sign the document. It wasn't his fault that he wasn't scheduled… his manager literally forgot about him. What can he do? The manager couldn't believe his attitude and told him to think about it. Anyways…
The employee did well; what can I say? I like how he stood up for himself and proved the manager wrong. The boss was shocked: maybe he was trying to pass the blame to the boy because he couldn't admit that he had made a mistake. There's nothing wrong with that; it can happen to all of us. If the manager had done so, this whole conflict could have been avoided.