What's the meaning

of in passing here? Does it mean while they pass each other?

poster1: "Do you think the cabinet was too large for them to lift and at least move it to the curb? Pictures of Mr. Tamagotchi (a neighbour)? Is he very small?"

poster2: "I have only seen him in passing but my impression is that he owns bicyle clips and corduroy, and he works in a library. He has long hair and glasses and dresses very poorly."

Thanks a million!