Cat threw up food. It looks semi solid. He doesn't want to eat atm. Do you think it's hairballs?

He's walking around fine and everything. The food came out looking sort of like a little log. Afterwards he threw up two small bits of liquid that was the color of the food. He had been eating dry food yesterday so I was thinking the hairball and the dry food combination made him sick. Or he ate too fast. I tried to give him some wet food but he walked away from it. Should I be worried now? What can I do for him?