According to Dictionary.com
sec⋅u⋅lar
/ˈsɛk
yə
lər/ Show Spelled Pronunciation
[sek-yuh-ler] Show IPA Pronunciation
–adjective 1. of or pertaining to worldly things or to things that are not regarded as religious, spiritual, or sacred; temporal: secular interests. 2. not pertaining to or connected with religion (opposed to
sacred ): secular music. 3. (of education, a school, etc.) concerned with nonreligious subjects. 4. (of members of the clergy) not belonging to a religious order; not bound by monastic vows (opposed to
regular ). 5. occurring or celebrated once in an age or century: the secular games of Rome. 6. going on from age to age; continuing through long ages. –noun 7. a layperson. 8. one of the secular clergy.
So, your teacher is not 100% wrong. But probably needed to further clarify. It is when people do not believe that religious activities or beliefs have any bearing on something. So, in some respects, and in some interpretations of what your teacher said, they were correct.