Wendy Marvin from Matrix Roofing and Home Solutions had to say in response to your question:
It’s very difficult to tell from a single photo. This appears to be showing one layer of shingles. However, what often happens is that a second layer can be “cut back” to only be found further up in the roof? Perhaps a video while the roofer is inspecting is in order?
Adding a 2nd layer to tear off and disposal is a hefty additional cost to the homeowner. The roofer should be willing to document via picture or video, why they believe there is a second layer.
Hope this helps!