I think it's the kerning, or when we are being funny, 'keming' which is a visual pun (when kerning goes wrong, kerning and keming are homographs).

Ironically, the text I had the hardest time reading on their example page was the name of the font itself: Comic Mono has all the letters running together.

Unfortunately Comic Shanns doesn't render its own name in the examples that I see, but you can see that the capital C has another pixel between it and the next letter.

ETA: Author generated this font via the use of some scripts, which are inline near the bottom. There's a line about target_width in there, I'm curious what happens if you bump that from 510 to 530...

My old coworker Shannon Miwa created it! She's great.