Woooah, okay as a university student I just have to comment on this.
This professors actions are in no way questionable. A College/University is a place where intelligent debate should absolutely be welcomed. Whether it be about politics, religion, or whatever topic may arise.
I don't understand why you think the professor did something wrong by letting a religious debate occur in a college setting?
I certainly don't think that a college professor is in any way responsible for stopping "impertinent discussions" when they are regarding the subject matter at hand. In fact, I'm sure this professor was happy to see this student engaged in conversation and defending/arguing their beliefs, rather than silently sitting in class listening.
In some of my classes it's like the prof is pulling teeth trying to get debate & discussion out of students.
I'm just confused as to why you think a college isn't the right place for an intelligent intellectual debate.