So if the actor speaks the line correctly and the closed-caption people don't transcribe it properly, is it bad grammar?

I was watching the first episodes of season four for "Warehouse 13" and during the episode "Endless Wonder" Claudia says that "Artie is protecting everyone" Myka says "but from whom." Myka is a literary genius who grew up in a bookstore with her bookseller parents. Myka used good grammar by properly saying "whom." The person who did the subtitles says "from who." Someone must have called them on it because by the time the next episode ran, and they ran the recap vignettes  for what had occurred during previous episodes, the closed-capitioners had corrected the "who" to "whom."."