We need matrix-multiplications for running neural networks, and neural networks find better ways for matrix-multiplications...

DeepMind's Game-Playing AI Has Beaten a 50-Year-Old Record In Computer Science

"[...]Overall, AlphaTensor beat the best existing algorithms for more than 70 different sizes of matrix," concludes the report. "It reduced the number of steps needed to multiply two nine-by-nine matrices from 511 to 498, and the number required for multiplying two 11-by-11 matrices from 919 to 896. In many other cases, AlphaTensor rediscovered the best existing algorithm.