I would read that as emphasizing that if multiple models of a fireteam are visible to you, you don't get an ARO against each one of them, and the rules are emphasizing that very clearly.
Stealth specifies that the model Indeed, the sense seems to be for reinforcing that you can only react once with a given miniature/marker against one enemy order. That's why forcing a useless ARO in the first short order lets you act safely with the second.
