I doubt it would be treated as theft by finding as QF still controls the points even if they are sitting in your account (unlike the owner of a bag of $250,000 in cash when you walk away with it).
All that matters is that they are not the persons. hat a mistake was made in awarding them is I think irrelevant.
= Theft by finding.
If you reasonably should not have known that they are not yours, then using them technically becomes theft.
There was a case for example of a CEO who was awarded bonus shares as part of his package. By mistake they went to another person.
The value of the shares was substantial.
It was not for many years that they mistake was notice when the CEO went to leave the comparing and then discovered that his bonus shares had gone missing. An investigation then tracked them down.
The recipient of the shares had sold then and was found guilty of theft. From memory they went to jail.
A few thousand, or even tens of thousands, of points one could claim to have not to realised about. With 3 million it would always be assumed that you will have known that they were yours.
The interesting point (and lawyers may care to comment on) is whether being FF points if somehow that makes a difference as compared to cash, shares, etc..
Materialising the 3 million points would however cryrstalise the value of the points making it difficult for one to argue that they had no value.