It's not clear. Your own bias makes you think that's clear. The alternative is that the instructor believes it's plagiarism. This means they thinks they've seen what's in front of them before exactly as worded in uncommon scenario or they sees an odd discrepancy between that paper and prior work of hers. Several people have already showed up in the comments pointing this out with one person catching real cheaters using this method. That validates it's a hypothesis that must be ruled out as we determine what caused the decision.

Unfortunately, we don't have enough data to do that. All we can be sure of was their evidence appears weak, how they handled it should get them reprimanded/fired, and we only heard one side of the story by an individual with extreme bias on this sort of thing which pervades the whole article. So, I'd like to hear what the professor or other people there said about that event, the professor, and her. Past that, I have to address it conditionally like "If professor did this, then it might have been reasons X or Y with terrible corrective action taken. Source leans toward X based on personal experiences but no data to support either."

Note: There's also other forms of discrimination based on language besides race in terms of what you expect of different kinds of skill levels, institutions, local dialects, etc. I've had many experiences with discrimination based on how I write or speak from white and black people of both genders with women doing it much more to me than men. In the white cases, race usually had no element in it since I'm white but they were still judgmental pricks with their own biases with impact on my future. It's why I'm pro-merit and anti-superficial.

Edit: Had to change some pronouns because my own bias made me assume something. Bias is that sneaky!