** No bonus wager requirements were active or used
This is the only relevant aspect. If multiple accounts were made from the same computer and both used a bonus, it's reasonable to assume it's the same person attempting to abuse the bonus.
Are you positive that neither account had ever received any bonus?
Even if Op story is 100% legit, it will be very hard to convince the casino that Op is telling the truth.
If they have reasons to believe someone is trying to cheat their bonus, created multiple account with the same IP or display some sort of weird behavior.
But I don't think that grabbing winnings/deposit of the users is justifiable practice even then.
It is funny that they weren't investigating/blocking you earlier, but when you won, their security system suddenly woke up.
