Thank you.
So, is "zero spacetime curvature" the same as "zero intrinsic spacetime curvature"?
Yes, obviously.
Wouldn't that imply that a uniform gravitational field, with zero intrinsic spacetime curvature, is the same as Lorentzian space, with zero spacetime curvature?
Uniform gravitational field does not have zero (intrinsic) curvature, the Riemann tensor is not null, so where did you get the idea above?