Rather, the existence of black holes demonstrates that gravity is not renormalizable.

The last sentence in the paper:

"It seems that gravity is a low energy effective field theory description of something else that is not a quantum field theory."

QFTs like QED and QCD are renormalizable. This is a technique used to eliminate the infinities that arise in calculations from self-interaction. For a very long time, renormalization was viewed as hocus pocus (including by the person who discovered it). Later, mathematicians were able to provide a solid theoretical foundation for it.......but only as an effective field theory valid at particular size and energy scales.

Net net, the standard model is an approximation of something more fundamental. Gravity being nonrenormalizable shows that "something" is not a QFT.