No only that, its only relevant if you have diabetes/pre-diabetic markers. If you're not then it's as relevant to you as being concerned about lactose if you're not lactose intolerant.

It’s relevant, but also easy to measure. GI is a guess at what the product will do to your blood sugar. A diet high in fiber they included oatly with a meal is going to give a very different insulin response than oatly in isolation which will likely be different again when compared to pure maltose. I am not diabetic and had fun measuring my blood sugar for a while. Full meals with a lot of fiber, even if they included high GI foods didn’t do a lot to my blood sugar compared to high GI foods in isolation. So, as a diabetic, you just have to know how your body handles some foods and how best to consume them (or not).

It's true that if you eat fat, protein and fibre alongside sugars, the effective GI of the sugars is reduced.

But I really don't think see how that makes measurements of individual foods misleading. How is it any different than individual foods being labelled with calorie counts and macro-nutrient figures?

Edit: I think the article uses the high GI of a sugar ingredient to claim that Oatly is bad - yes, this is misleading; the GI of the whole product is what matters.