When A. Einstein realized, in 1907, the incompatibility of his ideas with the Newtonian's concepts about gravity he tried to reconcile his ideas with the special relativity and find out a new form to treat gravity using the equivalent principle as a light. Even when H. Minkowski found the geometry meaning of the Lorentz transformation A. Einstein did not use it at all in 1911.The paper is mainly about Einstein's 1911 assumption that gravity alters the speed of light. This assumption was later abandoned.
The author is trying to credit Einstein with good ideas, not undermine him. But look at what this says.
Everybody knew in 1907 that relativity was inconsistent with gravity. H. Poincare wrote a famous paper in 1905 proposing a relativistic theory of gravity. I think H. Lorentz did also. If Einstein just realized it in 1907, it is because it took him two years to understand from others.
Relativity caught on big after Minkowski published his geometric version in 1907, referencing Poincare's 1905 version. It is that geometric version that is in use today, not Einstein's version. But note that four years later, in 1911, Einstein was still rejecting it.
I wrote a book about this. See this blog post, for more about how Einstein rejected geometric relativity. When someone credited Einstein with a geometrical interpretation, Einstein published a letter in 1911 denying it.
It is baffling how anyone could credit Einstein for special relativity, or for recognizing the need for a relativistic theory of gravity. As you can see, he was well behind others.