Well no, the actual wording is being misinterpreted. The terms used are partially:

only be earned in that season, and will not be available in later seasons."

As written this means that skins can't return in future passes. That's true. It can also be inferred that previous battle passes can never return.
It says nothing about the individual cosmetics and sets from previous passes being put up for direct purchase in the item shop, which does not explicitly use the season as a gauge for content. The closest it comes is showing when cosmetics were first introduced. In that instance the "promise" still stands: the cosmetics are available outside of the seasonal structure of a battle pass, and they're purchased, not earned.

Fallout 76 began selling season pass cosmetics in their cash shop, and no one challenged Bethesda on it. Why would you? Those cosmetics were potentially free during the season, and sold for full price if you bought them in the cash shop. Players who were there got things like the greenhouse set for only their time. Others paid for it. The same thing would be argued for this game should it happen.

Now if you're speaking on the legality of it, I'd love for you to find a case where this practice was actually challenged. I'm going to guess it hasn't happened yet, so we simply can't know how a judge would rule.