When you use custom close reasons, it first appears below the question as a comment. And on receiving further close votes for that particular reason, the auto-added comment gets auto-upvoted.
On reaching the required votes to close the question, and if the majority of the votes are for that custom given reason, then the question will be closed and the banner will then show a default text:
This question does not appear to be about English language and usage within the scope defined in the help center.
Usually we write the exact reasons when we use the custom option. But I suppose in this case it was not clear what to write in there.
And usually the auto-added comment stays under the question for a while. Maybe it was removed by the original close voter.
Should we use such blank close reasons?
But what to do when we are not sure what reason to write?
When I find off-topic questions for which I cannot pinpoint the reasons, I use the default text shown above as the custom reason.
Also, when you get to 10K, you can see a list of custom close reasons used in the last 90 days. It shows me that the default text and it's various paraphrased variants are the most popular ones.