You're likely right. If I recall correctly, the decision to do a refund is entirely steam's and the publisher has no choice but to foot the bill because of steam's tos. To add to that, refunds don't include the 30% cut steam makes on the sale, so the publisher actually loses that money if they have to cover a refund.

Say the game costs $50. Steam takes $15 of that and the other $35 goes to the publisher. If steam decides a refund is in order, the publisher must pay back all $50.

So yeah, Sony was losing money for every copy that got refunded due to a reason steam found justified. Given the sheer publicity of this whole thing, someone up top probably realized that if they carried through with it it'd cost way more than the pennies they'd squeeze per player by force linking their accounts.

People shit talk steam being a tyrannical monopoly all the time, but they are pretty consistent when it comes to treating their users fairly. This is a prime example of steam using its leverage to stop something really shitty.