Of course, we have no idea of the context. But if it was anything like the linked video - and it could have been worse - it’s perfectly understandable why students would be surprised and perhaps upset.
If you disagree, its worth asking yourself, what reaction would you expect if you were a chinese professor enunciating the word “cunt” during a lecture, with no prior warning?
And if a Chinese professor prefaced the use of that word with an explanation about that word's usage in another language, I would find that a very memorable educational experience. That's it. I don't need to be warned about a sound because a similar sound with a different meaning is used in negative ways.
Perhaps you don’t - that’s fine. But can you see why other people might need such a warning?
If you were teaching a foreign language word with a similar sound to “motherfucker” what reaction would you expect from your class of 18-21 year olds?
As far as saying "motherfucker" - I'd expect chuckles from any students paying attention. Then class would continue. It's not like students haven't heard all of these words before.
I was surprised by the linked video though, it could have done with a prior warning in my opinion.