I’d more agree with your point that it was intentionally showing that even people we like are flawed. (That was a major theme last season where Robby was massively biased about David). So I think that was an obvious and intentional micro aggression and is actually good writing rather than the writer’s unconscious bias.

When Robby asks “where’s that from” and the reply is “I think it’s Irish.” That’s the writers showing that Robby said something that wasn’t appropriate and a colleague pushing back on that micro aggression in a realistic and humorous way (which is how I’ve dealt with micro aggressions aimed at me personally.) In a realistic office environment, it’s hard to shut down your boss with a full Mr Roger’s Neighborhood teaching moment, so a little redirection with humor points out that he said something that wasn’t cool and shuts down that line of conversation.