That's a very odd position for a professor to take. Maybe that's why European science education has such problems. It's at about the same level as a literature professor telling you that you are not to come up with a theory not already presented in lecture. It's just...strange.

Of course it happens, and probably more often than I would like it. But even though there is some logic in not debating a data point without a similar body of data, that's not much of an excuse.

Complain to the dean.