You're still approaching this with the background knowledge of what this is. If you've never seen this, you can only guess, and there are a couple of options.
I've been terminally online for the better part of the last 2 decades, yet I've seen this way of writing for the first time only ~5 year ago or so, and I still remember simply not knowing what it is. The first reaction is that it's simply a typo - the author mistyped - the dot should have been a digit or perhaps not be there at all.
For most of the world that is even more ridiculous than using dot as decimal space separator or writing dates with month not in the middle place.
Even Americans I work with don't write it like that when doing quick draft discussion, as they know it's confusing to others.
I only know it's a thing because I watched some math-related edu shows. Didn't even see that when I briefly worked in US.
Come on, let's be fair—nothing else will ever be as ridiculous as that!
- "a gallon". Not purely US thing but almost. It can be anything from 3.8 to 4.4 liters, depending mostly on what are you measuring.
- writing digits. Is it "1", is it "7", is it "i", is it "l"? Why do it to yourself, while their printed fonts are pretty much the same as everywhere else...
It might be moderately intuitive to English native speakers because of oral usage like “point one three eight”, but that’s also not a thing in many other languages.