Why does Mr Frank call Taplow a slacker?

Taplow had told Frank that should results be favourable, he would choose science over the classics. Frank himself teaches science, and his experience students who are unwilling to put in the hard work that the classics require, choose science as an easier option in order to slack off or relax. That is why he assumes that Taplow must be a slacker as well. However, Taplow resists this definition saying that he actually is very interested in science.