Computer Vision(opencv) vs deep learning

Object detection can be done using open CV and deep learning. But I and not able to get what’s the difference between the two. Deep learning involves training that enables it to learn and detect objects. How does the OpenCV do that? Is there some kind of model trained in it?

OpenCV most likely uses a trained NN under the hood.
See this link to see the options you have to configure the opencv detector.

Does it mean that the detection done with an open cv is also an application of deep learning?

Please see this

I went through the code and as far as I get, they have used a pre-trained model and operated that using openCV. The same logic of the face net is used to calculate the difference and comparing with the threshold. Am I right?

Your understanding is correct.