Are the pores under a face mask actually oil?

I’ve been trying out new skin care routines lately and tonight I tried out a clay face mask. After it dried out, I noticed that my pores were visible under the mask.
Are these really pores, or the oil that is drawn from them coming to the surface under the mask?

The product I’m trying said that it purged pores and cleansed, etc. I’m wondering if this is the oil from clogged pores or something.