Just an example and perhaps it's not what you're thinking of but it's what I'm getting at (horribly apparently): say someone meets a person who by appearance looks to be of Asian decent. That person strikes up a conversation with this new person, and to 'relate' to them, they talk about some movie they saw recently starring an actor of Asian decent or wants to discuss their favorite Japanese dish or something like that, when the person they're talking to may very well not have in any way any sort of interest in those sorts of things (and isn't of Japanese decent to start with).
The person bringing those up doesn't bring up similar topics with people of their same race.
The intentions are positive, and not directly harmful like what racism is often associated with, but it's based on what they assume about them from what they've known prior and shows little regard for what makes that individual who they are.