After reading up, I am going to support what Barracuda93 on what he said, with a slight twist.
While I don't think the person getting the op-up should be "entitled" to lounge access, CX would be stupid not to offer to that person. That is in fact a great way to introduce that person (presumably somebody with some status or potential) the full experience of business class. Maybe he can't/won't afford it now, but who knows? Maybe he will be a more loyal customer after this experience?
And honestly, I don't buy into the revenue management argument of it. First of all lounge is mostly fixed cost with minimum incremental cost for each passenger. The second thing is that capacities should have been carefully calculated with approximate yields (so hypothetically, a flight may have, say, 50-60% of the "enabled" (FF/Business ticket) passengers using the lounge). That should be the benchmark and an extra business class passenger per flight at any given time (or even 3) should not cost that much. Thirdly, if even the lounge is figured into the cost of a ticket, then it is basically the fault of revenue management and they really should ensure that business tickets are all ticket up (or now that they could have offer upgrade with money, similar to JAL domestic) to ensure that all business class are taken up. If as a last resort, an upgrade has to be made such that it does not generate the kind of revenue they would have estimated, then the cost of entrance to a lounge should be something to add-on, reminding them to do it better.
So actually, if you asked me if the person has the "right" to get in, I'd say no. But the fact that CX showed its fragile ways as a premium carrier, is also nothing to be proud of.