Uh, no. He says it's absurd to suppose it could act, "without the mediation of something else", but he didn't know what that was. Einstein later provided a model for that mediator with dynamic spacetime, but a gravitational field does just as well.
The rest of that passage reads, "Gravity must be caused by an agent acting constantly according to certain laws, but whether this agent be material or immaterial is a question I have left to the consideration of my readers."
Odd that that last bit is so often left out. Oh, wait... quote mining.
So, yes, that Newton. You know, the one who produced the Law of Universal Gravitation that gave the mathematical formula for calculating the force of gravity:
F = G(m₁m₂/r²)
You know, the law that explained the falling of apples to the ground in his back garden, and the orbits of the planets and their moons?