I'm a little confused by the expression "Albert Einstein’s theory of gravity."
Modern theories of gravitation are generally associated with Isaac Newton, whereas, Einstein is more widely known for his ideas on relativity. Certainly, Einstein's work related to gravity, but to use this expression with its unusual association and not have any explanation for its use just seems odd.
I suppose that's what happens when WT writers write about things they don't really understand. Maybe they fall into the category of people that think if you use Einstein's name in a sentence it makes you appear intelligent. I'm surprised they didn't also refer to "quantum mechanics" while they were at it!
That being said, you may appreciate that in a largely favorable review of the work cited, the Encyclopedia of Scientific Principles, Laws, and Theories by Robert E. Krebs, reviewers Adam M. Kiefer and Kevin Drace pointed out a flaw in this work, one that is particular relevant to the point under discussion. They comment that this second edition continues the "erroneous presentation of theories being built from laws."
Interesting! I bet the WT writer that lifted these blurbs in a failed attempt to appear smart wasn't aware of that!