Well, think that statement through a bit:

Grep reads through the entire file looking for patterns.

An LLM scans its neural net (in ways that I don't understand) which is kinda-sorta like having a huge index.

You can improve over Grep if you have an index; and the LLM has an index.

Thus, it's plausible that an LLM can be more efficient at reading its neural net (IE, index) than Grep reading the whole file.