Basically, it is becoming more common in English writing to use the masculine “hero” as gender neutral when the figure is a famous and/or historical figure.
If it is a fictional character, “heroine” is still widely used.
There’s been a wider trend of using gender neutral terms in the language. “They” as a replacement for “he” or “she”, for example, used to be improper but is now quite widely accepted and not only when speaking about a non-binary person.
Just because your English professors taught at a university, does not mean they are the final authoritative word on how the English language is spoken.
That's kind of the point: there isn't an authority on English. The closest we come is a bunch of English elites making up informal rules on grammar, spelling, and pronunciation and judging everyone else for not using their version. ... And a bunch of try-hards who enforce their arbitrary and often nonsensical 'rules '.