That one “who”

My professor once jotted a minor tweak on one of my (surprisingly to me) decent papers. I’d written something like this:

“For instance, anyone that eats marshmallows would probably also enjoy s’mores.”

Can you spot the mistake (overlooking the marshmallow reference in a research paper)?

My professor crossed out “that” and replaced it with “who.” The word refers to a person, so it deserves to be a who, not a that.

The bad thing is that now it bothers me when I see someone make this mistake. The good thing: I remember being the guy who did that.