Stopped reading at "some slavic shit"
Similarly, I took the author's "disdain" for slavic as not-real, but rather a meant-to-be-funny turn to avoid a detour into Romanian as the point of TFA was ultimately that the yeses in Romance languages generally derive from something like "this".
I am rather surprised you truly felt offended.
"because they’re on some Slavic shit."
Did Romania at some point get invaded by some other Slav people, is it merely Slavic language osmosis between cross-border dialects?
If the casus belli for US entry into WW2 was referred to as "Some shit the Japanese pulled" in a piece about history, wouldn't that give you pause?
It was an opportunity to teach a reader something, but the opportunity was exchanged for a popular short-cut expression. If found that somewhat irksome as well, even though it did not offend my cultural identity.
Let's try another version, some Mexican shit. Trump comes to mind? Yup! You got it.
I think it is worth expecting readers to expend a small amount of effort to try and assess a writer's intent, so that we might live in a world where people can use colourful language. Teasing someone is not the same as insulting them.
Moreover, as with any complex subject, there are possibly other limitations working in paralell (but still connected to the level of reading): the emotional state one’s in when it stumbles something in writing. Again, if one lacks a sufficiently mature reading skill, one tends to take things at face value, without making the obvious leap of understanding them within the larger context both of the text itself and the subject matter at hand.
It is difficult for others to determine your intent without you providing additional context. That you are reporting a fact is immaterial - the question in others' minds will be why you are reporting that fact, because they are trying to understand what you are trying to show with it. As I said in a previous comment, context and intent are important, and if you are unwilling to provide those yourself, you have to accept that people may misunderstand you. Complaining about those misunderstandings is not constructive, you should simply try and clarify your position.
The phrase "on some shit" comes from the United States, from urban AAVE (African-American Vernacular English). There's another commenter that refers to the phrase as 'hip hop lingo', which isn't too far off, but I think it's the wrong label.
The origins of the phrase are hard to pin down, but nowadays you'll see the idiom as "on some ____ shit", where you replace the blank with just about any noun or adjective. It has a fairly wide range of meaning, but the gist is 'acting ____', 'referencing ____', 'influenced by ____', 'in the style of ____' .
In this article, writing about Romanian language, saying, "[they're] on some Slavic shit" means "[they're] influenced by Slavic" or "[they're] referencing the Slavic style".