Meaning of "misuse of the word 'only'" in context

I am reading the book Learning Python by Mark Lutz, in which there's a passage I don't understand:

I also want to thank my original editor at O’Reilly, the late Frank Willison. This book was largely Frank’s idea. He had a profound impact on both my career and the success of Python when it was new, a legacy that I remember each time I’m tempted to misuse the word “only.”

Emphasis added. What does he mean?

It means that Willison, as his editor, corrected Lutz many times on Lutz's (mis-)use of the word 'only' in some context that he doesn't specify here. Lutz remembers Willison's legacy as an early supporter of Python each time Lutz stops himself from mis-using the word 'only' in a way Willison wouldn't approve.

"Only" is not a keyword or reserved word in Python, and so the author is probably referring to some egregious or incorrect use of the word "only" in English sentences, which use was corrected in some memorable way by the man he identifies as the original editor. Unless you have the original manuscript which contains the incorrect usage you're not going to be able to "get it."

May I suggest that if you are sufficiently interested, you might contact the author (his email is likely publicly available) and ask. No doubt he would enjoy sharing the story!