"Custom navigation" means I as a reader need to split my focus between learning how this thing works, and consuming the information presented, which is presumably the goal of this page. I can't say for sure because the instant my screen started scrolling the opposite axis I smashed the back button.
Pick a lane: this kind of stuff is fine as a "design" showpiece, but if the goal of a page is to convey information, why introduce distractions over sticking with familiar patterns?
in other words, it's not that deep. The site is fun and you can figure it out.
Sure, I am perfectly capable of figuring out the site. But I won't trouble myself with it. My loss it seems!
And lastly, the person I was replying to claimed the design "fit the content so well" or something to that effect, which communicates a certain depth, contrary to your claim. I was genuinely trying to understand what I'm missing out on.
and this is different from your point which maybe is "how does this help me understand fonts better?" which is fair.
I can understand the perspective that something whimsical might appeal to a certain group and even enhance the experience; in fact I usually enjoy non-standard game designs, and in general I really appreciate subversion in most media I consume. I think however when it comes to educational or info-dense resources, I prefer the UX to be minimally distracting.