だ is what linguists call the copula: https://en.wikipedia.org/wiki/Copula_(linguistics)
In English, it's words like "is", "was", "are" or the verb "be". It follows the rules of linguistics, not mathematics, so there shouldn't be pressing need to stress its non-commutativity.
In most Japanese lessons in English, when you are introduced to だ/です/である, it is simply explained as being like "is", or if they've already set a rule that sentences end in verbs, it's introduced as the verb "to be". That conveys, rightly or wrongly, all the things English speakers understand about "is".
This Japanese lesson starts with the assumption that part of the "だ" hiragana looks like "=", which I already don't agree with! Even the dakuten (゛) on the character looks more like an equals than the swooshy bowl they're comparing to "=".
It then says that だ is comparable to equality and mathematical equations, rather than like the lingual is/are/be, and then has to qualify that the equality is non-commutative. They could've saved time by not making that comparison, and instead comparing with is/are/be, which English speakers already understand is not commutative. "John will be early" != "Early will be John" (unless Yoda, you are)
That's helpful context, but I didn't really consider them separate contexts for the purposes of using context clues to try to understand it. I thought you didn't know what that part might mean. What did you mean?