They are both true, of course.
How does the under side of a wing produce lift? By pushing air down.
How does the upper side produce lift? By reducing the pressure.
If you think back to your ppl aerodynamics, you will remember about 2/3 of the lift coming from the upper surface and 1/3 coming from th eunder side.
Some one showed that the spin relied on the lift from the underside and arrived at a figure of very close to this 1/3.