It's not silly: devout Christians have had differing interpretations over whether the Bible teaches that or not, just as they have had differing interpretations over whether the Bible teaches a 6,000-year-old universe. But what the Bible teaches is quite beside the point: the issue concerns what this particular student believes about mathematics, just as the real-life case concerns what particular students believe about biology. In all likelihood the professor has written many letters of recommendation for devout Christians who accept evolution.
would be fine as long as he can show the math professor the proper equations.
Fine to you, but if it's not fine to the professor, should he be compelled to say it's fine?