Here's the definition of meta -
pertaining to or noting a story, conversation, character, etc., that
consciously references or comments upon its own subject or features,
often in the form of parody:
A movie about making a movie is just so meta—especially when the
actors criticize the acting.
: showing or suggesting an explicit awareness of itself or oneself as
a member of its category: cleverly self-referential
Something is meta (and self-referential) if it is about itself.
In your context, the detective focuses on the bar's name itself (which is ironically named "The Bar") rather than any other feature of the bar.
Another example of meta -
In a meeting, time spent discussing the meeting itself - how long it will last, who will talk first, whether everyone can see the screen - is meta. It's about the meeting, rather than being about the topic the meeting is supposed to be about.