I saw this question, which piqued my interest as I'd not seen the tag used before. It was closed as off-topic, which leads to my question; what would be an on-topic ascii-art question? If there aren't any, then why is the tag still available for selection?
what would be an on-topic ascii-art question
The ascii-art tag (just click on it - It's really a link) shows a number of questions that weren't closed as off-topic (although a few probably should have been). My first thought (and one that is represented) would be questions around figlet, which is locally installed software (on-topic) to create text-based ASCII art, of sorts.
Really, any locally installed software to create ASCII art would likely be on-topic (as long as it met all other criteria). It's just, as @JourneymanGeek said in the other answer, that the particular post you mentioned was about a WebApp, which is off-topic.