[jklein11]

You are a professor and unclear on the difference between harder and hardest?

[thot_experiment]

There are professors in non english speaking countries it turns out.

[aguacaterojo]

good chance he is a professor in a technical field and English is not his first language

[sodapopcan]

Absolute possible. They also could have just made a typo while typing a comment on a casual internet forum, which is also perfectly acceptable.