Genuinely curious, has Buffett said this before in an interview somewhere or have you asked him personally? OP wrote “seems to,” but your response suggests more confidence.
He has been quoted numerous times about avoiding having people front-run him over the last 50+ years. He negotiated special disclosure rules with the SEC at one point to avoid disclosing new positions quickly, IIRC.
There aren't any formal rules that he lives and dies by, but read "Buffett: The Making of an American Capitalist" by Lowenstein. Buffett -- or at least Lowenstein captures -- expresses concern for people buying before he does.