It’s happened to be before, not sure how/why though.

Took my phone in to get a price on replacing the cracked screen. Phone was about a year or so old, and never had Apple Care. The guy told me he’d just give me a new phone instead for the cost of the repair, which was like $80 I think. In and out in less than 10 mins.

I’ve also heard they do this if they accidentally damage your device during repair.