It certainly looks like they are specifying a maximum compensation for the relevant situation here.
But suppose it were entirely up to United. Whenever I've asked people what United should have done instead, "offer more money!" is really the only response I've gotten. Even if the amount were much higher, there could still be scenarios in which people would refuse it for whatever reason. And even if it were entirely up to United, that seems like very minor mistake, if you could call it that. And certainly nothing that should cause anything resembling "moral outrage." Particularly when their flight bump compensation is in line with all other major airlines.