I'm not 100% sure since I'm not the guy you responded to, but I think his situation is that he's listening to the audio in the same language as the subtitles, and they are different.

I've seen this happen when English subtitles were enabled for an English language movie I've been watching. Sometimes what is transcribed in the subtitles is different than what people are actually saying (though the gist is the same) even though both are in English.

In any case, this is clearly not something easily fixable by a website script.