the mesh is still snapped even i turned off snapping i have been following YanSculpts' tutorials and had issuses making eyelash.
after i made vertex snapped on the face mesh with snapping on face mode, and then tried to extrude the edge. but when ive done it, the face itself was still snapped on the face.
It looks like you have a shrink-wrap modifier on your mesh. It's not uncommon to use that when retopoing.