Nobody wants to be bothered on a Friday afternoon at work. It's just part of the human experience. We have our eyes on the weekend, and we don't want anything to get in the way of that. Everyone who works a monday through Friday job knows that you're mentally checked out at the end of the week. You're not going to start any big tasks, because you'll just have to pick them up on Monday morning. You're making plans for what you're going to do in the weekend, and your brain is halfway out the door. Humans are simple creatures. Our motivation waxes and wanes throughout the week, and you just have to ride that wave and try not to judge it too hard.
Problems arise when bosses try to micromanage what we're doing. They are too comfortable with the amount of control that they have, and they want to exert it over you. Some people just want to watch the world burn, and this boss was one of those people. A huge part of management is learning how to cater to the needs of your employees. Yes, you're in charge, but people do their best work when they feel encouraged. And you don't feel very encouraged by being kept late on a Friday afternoon. This is a breach of the work social contract in so many ways. But that didn't stop this boss.