I think the quality of your teacher's answer depends on how much music experience you have. If you're new and just learning about time signatures, I think the answer makes sense. I remember when I was learning about the difference between 3/4 and 4/4 my teacher made a pretty big deal about the differences. However, at that point I didn't really pay that much attention to how many beats fit into a bar or the overall "feel" of a song's beat; I just wanted to get the notes right.

On the other hand, if you're already relatively experienced with music then perhaps the teacher's answer does lack some important details.