Why does this search query not return the expected result?

The following search query returns no code results in the repository:

However, the search term does appear in the repository, as you can see here:

Why does search fail to find it? Is it a bug in GitHub search? Does GitHub have a reliable way to search all plain-text file in a repository?

Can I take the lack of response (explanation) as an indication that this is a bug in GitHub search?