What grew under his skin?

So my friend had, what looked like a big pimple on the back of his leg. He said it was extremely tender and every time he sat down, it would hurt. The pimple had managed to grow right on top(or under?) a hair. It also looked like something of a dark color was in there because the head of the pimple wasn't white(It had a grayish color to it). So he decided to pop it. After applying a considerable amount of pressure, he said it popped with an eruption and something hard came out of the pimple. It had a texture much like that of a grain of sand. We both thought it was an ingrown hair even though we have never seen or heard anything about ingrown hairs. Does that sound about right?